Recommendation T.411

OPEN DOCUMENT ARCHITECTURE (ODA) AND INTERCHANGE FORMAT

INTRODUCTION AND GENERAL PRINCIPLES

CONTENTS

Introduction

1	Scope

2	Normative reference

3	Definitions

4	Conventions

4.1	Names of attributes

4.2	Names of attribute values

4.3	Component and component description

4.4	Introduction of terms

5	General concept of ODA

5.1	Purpose of ODA

5.2	Overall concept of ODA

5.3	Document processing model

6	Overview of the Recommendations in the T.410 series

6.1	T.411 Introduction and general principles

6.2	T.412 Document structures

6.3	T.414 Document profile

6.4	T.415 Open document interchange format (ODIF)

6.5	T.416 Character content architectures

6.6	T.417 Raster graphics content architectures

6.7	T.418 Geometric graphics content architectures

7	Inter-dependencies of the Recommendations

8	Conformance

9	Document application profile

9.1	General principles for defining a document application profile

9.2	Rules for defining a document application profile

Annex A - References to other Recommendations, standards and registers

Annex B - Relationships with other Recommendations and standards

Annex C - Correspondence between Recommendation T.73 (1984) and Recommendations in the T.410 series

C.1	Data stream format

C.2	Presentation capabilities descriptor

C.3	Attributes

Annex D - Principles for the assignment of ASN.1 object identifier values

Annex E - Use of MHS to interchange documents conforming to the T.410 series of Recommendations

Introduction

Recommendation T.411 is one of the T.410 series of Recommendations which has been prepared by CCITT COM VIII/WP 2 for the interchange of documents in the context of document architecture transfer, and manipulation.

This series of Recommendations specifies a document architecture (known as the "Open Document Architecture" ODA) and an interchange format (known as the "Open document interchange format" ODIF).

The T.410 series of Recommendations consists of:

-	Rec. T.411: Open document architecture (ODA) and interchange format - Introduction and general principles;

-	Rec. T.412: Document structures;

-	Rec. T.414: Document profile;

-	Rec. T.415: Open document interchange format (ODIF);

-	Rec. T.416: Character content architectures;

-	Rec. T.417: Raster graphics content architectures;

-	Rec. T.418: Geometric graphics content architectures.

Note - At present, there is no Recommendation T.413

Other Recommendations may be added to this series.

The T.410 series of Recommendations supersedes Recommendation T.73 (1984)

Development of the T.410 series has been in parallel with:

-	ECMA-101: "Office document architecture";

-	ISO 8613: "Information processing - Text and office systems - Office document architecture (ODA) and interchange format".

1	Scope

1.1	The purpose of the T.410 series of Recommendations is to facilitate the interchange of documents.

In the context of the T.410 series, documents are considered to be items such as memoranda, letters, invoices, forms and reports, which may include pictures and tabular material. The content elements used within the documents may include graphic characters, geometric graphics elements and raster graphics elements, all potentially within one document.

Note - The T.410 series is designed to allow for extensions, including typographical features, colour, spreadsheets and additional types of content such as sound.

1.2	The T.410 series applies to the interchange of documents by means of data communications.

The T.410 series provides for the interchange of documents for either or both of the following purposes:

-	to allow presentation as intended by the originator;

-	to allow processing such as editing and reformatting.

The composition of a document in interchange can take several forms:

-	formatted form, allowing presentation of the document;

-	processable form, allowing processing of the document;

-	formatted processable form, allowing both presentation and processing.

The T.410 series also provides for the interchange of ODA information structures used for the processing of interchanged documents.

Furthermore, the T.410 series allows for the interchange of documents containing one or more different types of content, such as character text, images, graphics and sound.

1.3	This Recommendation:

-	introduces the T.410 series as a whole;

-	gives the references necessary for all the Recommendations pertaining to this series;

-	defines terms used in the context of the T.410 series;

-	presents the concepts of the document architecture;

-	gives an overview of all the Recommendations in the T.410 series;

-	describes the inter-dependencies of these Recommendations;

-	defines conformance to the T.410 series;

-	gives rules for defining document application profiles.

Annex A lists other Recommendations, standards and registers to which references are made, but that are not indispensable for the application of the T.410 series.

Annex B describes the relationships of the T.410 series with other Recommendations and standards.

Annex C describes the correspondence between Recommendation T.73 and the T.410 series of Recommendations.

Annex D establishes the Principles for the assignment of ASN.1 object identifier values in the T.410 series of Recommendations.

Annex E defines the use of MHS to interchange documents conforming to the T.410 series of Recommendations.

2	Normative references

The following Recommendations and International Standards contain provisions which, through reference in this text, constitute provisions of the T.410 series of Recommendations. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this Recommendation are encouraged to investigate the possibility of applying the most recent edition of the Recommendations and standards listed below. Members of IEC and ISO maintain registers of currently valid International Standards.

The following references are applicable to the whole of the T.410 series of Recommendations.

-	Rec. T.4 (1984): Standardization of group 3 facsimile apparatus for document transmission

-	Rec. T.6 (1984): Facsimile coding schemes and coding control functions for group 4 facsimile apparatus

-	Rec. T.50 (1984): International alphabet No. 5

-	Rec. T.60 (1984): Terminal equipment for use in the teletex service

-	Rec. T.101 (1984): International interworking for videotex services

-	Rec. X.208 (1988): Specification of abstract syntax notation one (ASN.1)

-	Rec. X.209 (1988): Specification of basic encoding rules for abstract syntax notation one (ASN.1)

-	Rec. T.412 (1988): Open document architecture (ODA) and interchange format - Document structures

-	Rec. T.414 (1988): Open document architecture (ODA) and interchange format - Document profile

-	Rec. T.415 (1988): Open document architecture (ODA) and interchange format - Open document interchange format (ODIF)

-	Rec. T.416 (1988): Open document architecture (ODA) and interchange format - Character content architectures

-	Rec. T.417 (1988): Open document architecture (ODA) and interchange format - Raster graphics content architectures

-	Rec. T.418 (1988): Open document architecture (ODA) and interchange format - Geometric graphics content architectures

-	ISO 2022 (1986): Information processing - ISO 7-bit and 8-bit coded character sets - Code extension techniques

-	ISO 6429 (1983): Information Processing - ISO 7-bit and 8-bit coded character sets - Additional control functions for character-imaging devices1)

-	ISO 6937-1 (1983): Information processing - Coded character sets for text communication - Part 1: General introduction

-	ISO 6937-2 (1983): Information Processing - Coded character sets for text communication - Part 2: Latin alphabetic and non-alphabetic graphic characters

-	ISO 6937-3 (1983): Information processing - Coded character sets for text communication - Part 3: Control functions for page-image format1)

-	ISO 8601: Data elements and interchange format - Information interchange - Representation of dates and times2)

-	ISO 8632-1 (1987): Information processing systems - Computer graphics - Metafile for the storage and transfer of picture description information (CGM) - Part 1: Functional specification

-	ISO 8632-3 (1987): Information processing systems - Computer graphics - Metafile for the storage and transfer of picture description information (CGM) - Part 3: Binary encoding

-	ISO 9541-1: Information processing - Font and character information interchange - Part 1: introduction (2)

-	ISO 9541-2: Information processing - Font and character information interchange - Part 2: Registration and naming procedures2)

-	ISO 9541-5: Information processing - Font and character information interchange - Part 5: Font attributes and character model2)

-	ISO 9541-6: Information processing - Font and character information interchange - Part 6: Font and character attribute subsets and applications2)

3	Definitions

For the purposes of the T.410 series of Recommendations, the following definitions apply:

3.1	active position

The point at which the action specified by the next character is to be effected.

1)	Under revision.

2)	To be published.

3.2	aligned around

A tabulation alignment that positions the sequence of character images for a specified character string such that the position point of the character image of the first instance of a specified group of characters within that string is positioned at the tabulation stop.

3.3	aspect ratio

The ratio of the dimension of a pel array in the direction of the pel path to the dimension on the direction of the line progression.

3.4	assured reproduction area

The rectangular area that remains on the nominal page after deducting an agreed allowance for edge losses.

3.5	attribute

An element of a constituent of a document that has a name and a value and that expresses a characteristic of this constituent or a relationship with one or more constituents.

3.6	available area

The area determined by the document layout process into which the content portion is formatted by the content layout process.

3.7	basic component

A basic logical or layout object, or an object class from which basic logical or layout objects may be derived.

3.8	basic layout object

An object in the specific layout structure that has no subordinate.

3.9	basic logical object

An object in the specific logical structure that has no subordinate.

3.10	basic measurement unit (BMU)

A unit of linear measurement equal to 1/1200 of 25.4 mm.

Note - A locally defined scaling factor may be used to map the document to a particular imaging device.

3.11	basic value

An attribute value, a control function parameter value or the value of any other capability that is unconditionally allowed in document interchange in the context of a given document application profile.

3.12	binding

A pair comprising an identifier and a value, where the value may be of any type, may be specified by an expression, and is accessed through use of the binding identifier.

3.13	block

A type of basic layout component that corresponds to a rectangular area within a frame or a page.

3.14	bottom edge

The edge of the positioning area of a basic layout object that is in the direction of the line progression.

3.15	bottom left corner

The corner of a layout object that is least progressed in the horizontal direction and most progressed in the vertical direction of this layout object.

3.16	bottom right corner

The corner of a layout object that is most progressed both in the horizontal and vertical directions of this layout object.

3.17	centred

1)	The result of a layout or imaging process that positions the sequence of character images for a line such that the distance from the line home position to the position point of the first character image is approximately equal to the distance from the escapement point of the last character image to the end edge of the positioning area.

2)	A tabulation alignment that positions the sequence of character images for a specified character string such that the distance from the position point of the first character image to the tabulation stop is approximately equal to the distance from the tabulation stop to the escapement point of the last character image.

Note - The term "centred" is also used in the parameter "alignment" of the attribute "position" and in the attribute "block alignment".

3.18	character

A member of a set of elements used for the organization, control and representation of information.

3.19	character base line

A line across a character image, in the horizontal direction when the character image is in its intended viewing orientation.

3.20	character image

The human perceptible rendering of a character on a presentation medium.

3.21	character orientation

The direction of the character base line relative to the character path.

3.22	character path

The direction of progression of successive character images within a line box.

3.23	character sequence

A sequence of characters intended to be presented as one or more lines.

3.24	characters spacing (for constant spacing fonts only)

The distance between the position points of successive character images when the inter- character space equals zero.

3.25	clipped array

The actual pel array to be imaged as determined by taking account of all clipping parameters.

3.26	complete generator set

A constituent of a document consisting of a document root object class description and at least one level of subordinate object class descriptions which are used to control the creation and/or modification of the set of object descriptions representing a corresponding specific structure.

3.27	component

An object or an object class.

3.28	composite component

A composite logical or layout object, or an object class from which composite logical or layout objects may be derived.

3.29	composite layout object

An object in the layout structure that has one or more subordinate objects.

3.30	composite logical object

An object in the logical structure that has one or more subordinate objects.

3.31	constant spacing

The characteristic of a font wherein the distance between the position point and the escapement point is the same for all character images.

3.32	constituent

A set of attributes that is one of the following types: a document profile, an object description, an object class description, a presentation style, a layout style or a content portion description.

3.33	content

The information conveyed by the document, other than the structural information, and that is intended for human perception.

3.34	content architecture

Rules for defining the internal structure and representation of the content of basic components in terms of a set of content elements, attributes and control functions, and guidelines for the presentation of the content.

3.35	content architecture class

The rules for defining the internal structure and representation of the content of basic components in one of a set of forms defined for each type of content element.

Note - Examples of content architecture classes are formatted form, processable form and formatted processable form in the case of character content elements.

3.36	content architecture level

An identified subset of the features pertaining to a content architecture class.

3.37	content editing process

The process that creates new content or modifies previous content.

3.38	content element

A basic element of the content of a document.

3.39	content layout process

The process that, interacting with the document layout process, consists of the formatting of content portions into available areas and the determination of the sizes of blocks in accordance with information contained in the presentation styles.

3.40	content portion

The result of partitioning the content of a document according to its logical and/or layout structure.

3.41	content portion description

A constituent of a document, representing a content portion that consists of content information and attributes to specify the properties of its content information.

3.42	content type

A category of content elements such as graphic characters, raster graphic elements and geometric graphic elements.

3.43	control function

An element of a character set that affects the recording, processing, transmission or interpretation of data, and that has a coded representation consisting of one or more bit combinations.

Note - Examples of control functions are Select Graphic Rendition (SGR) in character content architectures and Set Line Type in geometric graphics content architectures.

3.44	current layout position

The identification of a lowest level frame which is maintained during the layout process for each layout stream which occurs.

3.45	data structure

A set of data items and the relationship among them representing the whole or a part of a constituent.

Note - The data items constituting a data structure represent attributes of the document, the document profile, the component, the style or the content portion concerned.

3.46	description

A constituent that corresponds to a structural element.

3.47	descriptor

A data structure representing the document profile, an object class description, a layout style, a presentation style or an object description.

3.48	document

A structured amount of information intended for human perception, that can be interchanged as a unit between users and/or systems.

3.49	document application profile

The specification of a combination of features defined in the T.410 series, intended to form a subset to fulfil the requirements of an application.

3.50	document architecture

1)	Rules for defining the structure of documents, in terms of a set of components and content portions, and the representation of documents in terms of constituents and attributes.

2)	The structural information of a document consisting of the set of one or more of the following structures: specific logical structure, specific layout structure, generic logical structure and/or generic layout structure.

3.51	document architecture class

The rules for defining the structure and representation of documents in formatted form, processable form or formatted processable form.

3.52	document architecture level

An identified subset of the features pertaining to a document architecture class.

3.53	document body

The part of a document that may include a generic logical and layout structure, specific logical and layout structure, layout and presentation styles but excludes the document profile.

3.54	document class

A set of logical object class descriptions, layout object class descriptions, generic content portion descriptions, styles and a document profile, that specifies a set of documents with common characteristics.

3.55	document class description

The specification of a document class.

3.56	document layout process

The process that creates a specific layout structure in accordance with the generic layout structure and information contained in the specific logical structure, the generic logical structure and the layout styles.

3.57	document layout root

The composite object of the specific layout structure at the highest level of the hierarchy.

3.58	document logical root

The composite object of the specific logical structure at the highest level of the hierarchy.

3.59	document profile

A set of attributes which specifies the characteristics of the document as a whole.

3.60	document profile level

An identified subset of the features pertaining to the document profile.

3.61	editing process

The stage of a document processing that consists of the content editing process and the logical structure editing process.

3.62	end-aligned

1)	The result of a layout or imaging process that positions the sequence of character images for a line such that the escapement point of the last character image is positioned at the end edge of the positioning area.

2)	A tabulation alignment that positions the sequence of character images for a specified character string such that the escapement point of the last character image is positioned at the tabulation stop.

3.63	end edge

The edge of the positioning area of a basic layout object that is in the direction of the character path.

3.64	escapement point

A reference point associated with a character image that is used for positioning of the next character image.

3.65	external document class

A document class referred to by the document profile of an interchanged document containing no generic structure.

3.66	factor set

One or more object class descriptions which are used to factorise the attributes of object descriptions representing a specific structure.

3.67	filing

The storage of a document according to some defined method in order to facilitate retrieval of the document.

3.68	font

A set of character images normally with a common design and size.

3.69	font size

The height of the character images in a font.

3.70	formatted form

A form of representation of a document that allows the presentation of the document as intended by the originator and that does not support editing and (re)formatting.

3.71	formatted processable form

A form of representation of the document that allows presentation of the document as intended by the originator and also supports editing and (re)formatting.

3.72	formatting

The carrying out of operations to determine the layout of a document.

3.73	frame

A type of composite layout component that corresponds to a rectangular area within a page or another frame.

3.74	generic content portion

A content portion associated with an object class.

3.75	generic content portion description

A content portion description associated with an object class description.

3.76	generic-document

A structured amount of information intended for the interchange of generic structures, and optionally associated styles and content portions, for use in the processing of interchanged documents.

3.77	generic layout structure

A set of layout object classes and associated generic content portions.

3.78	geometric logical structure

A set of logical object classes and associated generic content portions.

3.79	geometric graphic element

A graphic element used to describe an image by geometric graphical means.

Note - Geometric graphic elements include those describing primitive geometric shapes such as points, arcs, lines.

3.80	graphic character

A member of a set of graphic symbols used for the representation of information.

Note - Graphic characters include simple alphanumeric characters (for example, accented letters) and pictorial characters (for example, mosaics).

3.81	graphic element

A content element that is capable of having a visual representation.

Note - Three types of graphic elements are distinguished in the T.410 series of Recommendations: graphic characters, geometric graphics elements and raster graphics elements.

3.82	hard line terminator

A line terminator that is intended not to be removed in a re-formatting process.

3.83	horizontal direction (of a layout object)

The direction in a layout object relative to which content architectures may define attributes determined using the horizontal axis of the page.

3.84	imaging order

The order of precedence of layout objects for imaging in the layout object to which they are immediately subordinate.

3.85	imaging process

The process of producing a document on a presentation medium in human perceptible form, making use of the document profile, specific and generic layout structures, presentation styles and content portions.

3.86	indentation

The result of a layout or imaging process that causes the sequence of character images for a line to begin at a distance from the line home position in the direction of the character path.

3.87	initial point

1)	The point associated with a basic layout object relative to which all line boxes imaged within that basic layout object are positioned (character content architectures Recommendation T.416).

2)	The point associated with a basic layout object relative to which all pels imaged within that basic layout object are positioned (raster graphics content architectures Recommendation T.417).

3.88	interchange

The process of transferring a document from an originating system to a receiving system.

3.89	interchange data element

A data structure representing a constituent of a document.

3.90	interchange format

The rules for representing a document for the purpose of interchange.

3.91	interchange format class

A form of interchange format suitable to a specific application.

Note - In the T.410 series of Recommendations, the defined classes differ by the ordering of the interchange data elements or by the coding.

3.92	inter-character space

An additional amount of spacing that is included between adjacent character images.

3.93	intersection

The common area of two or more layout objects that overlap each other partially or fully on the presentation medium.

3.94	item identifier

A string of characters preceding the first line of characters in a content portion that is used to identify the subsequent text.

3.95	justified

The result of a layout or imaging process that varies the width of the space character and/or the inter-character space to produce a simultaneously start aligned and end-aligned presentation of the text.

3.96	kern

The part of a character which extends beyond its position point or escapement point.

3.97	layout category

The association of basic logical objects with lowest level frames such that the content of these basic logical objects is placed in the appropriate frames.

3.98	layout object

An element of the specific layout structure of a document, for example, page, block.

3.99	layout object class

An element of the generic layout structure from which a set of layout objects with common characteristics may be derived, for example, pages with common headers and footers.

3.100	layout process

The stage of a document processing that consists of the document layout process and the content layout process.

Note - This is also referred to as formatting.

3.101	layout stream

A set of basic logical objects pertaining to the same layout category.

3.102	layout structure

1)	The result of dividing and subdividing the content of a document into increasingly smaller parts, on the basis of the presentation, for example, into pages, blocks.

2)	All layout objects and associated content portions forming the layout hierarchy of a document.

3.103	layout style

A constituent of the document, referred to/from a logical component, that guides the creation of a specific layout structure.

3.104	leading edge

The edge of a frame or block that is orthogonal to the direction of the layout path and that is met first, from the outside of the frame or the block, in the opposite direction of the layout path.

3.105	left hand edge

The edge of a frame or block that is parallel to the direction of the layout path and that is met first, from the outside of the frame or the block, in the direction at an angle of 270o counterclockwise relative to the direction of the layout path.

3.106	line box

A rectangular area within which a sequence of character images are positioned.

3.107	line home position

The point within a line box that is used for positioning that line box.

3.108	line progression

1)	The direction of progression of successive line boxes within a basic layout object (character content architectures Recommendation T.416).

2)	the direction of progression of successive lines of pels within a basic layout object (raster graphics content architectures Recommendation T.417).

3.109	lines spacing

1)	The distance between two adjacent reference lines within a basic layout object (character content architectures Recommendation T.416).

2)	The distance between two adjacent lines of pels within a basic layout object (raster graphics content architectures Recommendation T.417).

3.110	line terminator

A control function or combination of control functions that indicates the end of a line or the end of a character sequence.

3.111	logical object

An element of the generic logical structure of a document which may have a meaning that is significant to the application or user, for example, chapter, section, paragraph.

3.112	logical object class

An element of the generic logical structure from which a set of logical objects with common characteristics may be derived, for example, composite logical objects representing sections with a common internal structure.

3.113	logical structure

1)	The result of dividing and subdividing the content of a document into increasingly smaller parts, on the basis of the human-perceptible meaning of the content, for example, into chapters, sections, paragraphs.

2)	All logical objects and associated content portions representing the logical hierarchy of a document.

3.114	logical structure editing process

The process that creates a new specific logical structure or modifies a previous specific logical structure and allocates or re-allocates content to basic logical objects.

3.115	mandatory attribute

An attribute which, when applicable to a constituent, must be specified explicitly in that constituent.

3.116	nominal page

A rectangular area which, as assumed by the sender of a document, has the ideal size of the presentation surface.

Note - Examples of ideal sizes are given in ISO 216.

3.117	non-basic

A qualifier for attribute values, control function parameter values and other capabilities that are only allowed in document interchange in the context of a given document application profile if their use is declared in the document profile.

3.118	non-mandatory attribute

An attribute which, when applicable to a constituent, need not be specified explicitly; if the attribute is not specified explicitly in a given constituent, the attribute does not apply.

3.119	object

An element of the specific layout structure or of the specific logical structure.

3.120	object class

An element of a generic structure from which objects with common characteristics may be derived.

3.121	object class description

A set of attributes that specify the properties of an object class including its relationships, if any, with other components.

3.122	object description

A set of attributes that specify the properties of an object including its relationships, if any, with other components.

3.123	object type

A property of every component that specifies which attributes are permitted in the description to which it applies and indicates the role of the component in the document architecture.

3.124	orphan

One or more lines of text that is associated with subsequent text but isolated from it by a page or column boundary.

3.125	overhang

The result of a layout or imaging process that positions the sequence of character images for a line to begin at a distance from the line home position in the direction opposite to the character path.

3.126	page

A layout component that corresponds to a rectangular area used for presenting the content of the document.

3.127	page coordinate system

An orthogonal co-ordinate system whose origin is the top left corner of the page; its horizontal axis and its vertical axis coincide with the top edge and the left edge of the page, respectively.

3.128	page set

A composite layout component that represents a collection of pages or further page sets.

3.129	pairwise kerning

The distance between two adjacent character images depending on the combination of the two characters together rather than separately.

3.130	parallel annotation

Two sequential character strings that are presented in parallel, wherein the second string is used to indicate the pronunciation or interpretation of the first string.

3.131	partial generator set

A collection consisting of hierarchically related object class descriptions which are used to guide the creation of hierarchically related corresponding object descriptions but does not fully specify all specific structures that may be created.

3.132	pel array

A two-dimensional array of pels used to represent a pictorial image.

3.133	pel path

The direction of progression of successive pels along a line within a basic layout object.

3.134	pel spacing

The distance between any two successive pels along a line within a basic layout object.

3.135	picture element (pel)

The smallest graphic element that can be independently addressed within a picture; (an alternative term for raster graphics element).

3.136	positioning area

The rectangular area within a basic layout object within which the position points and the escapement points of all character images are located.

3.137	position point

The point relative to which the character image is placed i.e. the character is imaged with the position point at the active position.

3.138	presentation

The operation of rendering a document in a form perceptible to a human being.

3.139	presentation medium

The carrier of information in a form perceptible to a human being.

3.140	presentation style

A constituent of the document, referred to from a basic logical or layout component, which guides the format and appearance of the document content.

3.141	presentation surface

A two-dimensional presentation medium (such as paper, film, video display screen) on which the formatted form of a document may be displayed for human viewing.

3.142	processable form

A form of representation of a document that allows editing and formatting.

3.143	processing

The carrying out of operations on a document, including editing, reformatting, presentation, filing and retrieval.

3.144	raster graphics element

An alternative term for a picture element (pel).

3.145	reformatting

The carrying out of operations to determine the new layout of a previously formatted document.

3.146	reference area

A rectangular area within a basic layout object, with its side equal to the pel spacing and the line spacing, within which the main part of a pel is imaged.

3.147	reference line

A line through the line home position and parallel to the character path.

3.148	reference point

The point at the corner of the reference area situated in the opposite direction of both pel path and line progression and which is used for positioning a pel.

3.149	region of interest

A rectangular area within a virtual device coordinate space, with sides which are parallel to the axes of its coordinate system, surrounding those (parts of) geometric graphics elements that are intended to be imaged.

3.150	resource document

A generic-document containing one or more object class descriptions referred to by one or more object class descriptions of another document.

3.151	retrieval

The recovery of previously filed information.

3.152	right hand edge

The edge of a frame or block that is parallel to the direction of the layout path and that is met first, from the outside of the frame or the block, in the direction at an angle of 90o counterclockwise relative to the direction of the layout path.

3.153	scaled measurement unit (SMU)

A unit of linear measurement used for positioning and dimensioning layout objects and content elements on a presentation surface, its value being equal to the basic measurement unit (BMU) times the unit scaling.

3.154	sequential layout order

The sequential order in which layout objects are to be imaged when an imaging order is not specified.

3.155	sequential logical order

The sequential order in which logical objects are to be processed by the layout process.

3.156	sequential order

A convention for ordering the objects in a structure such that each object is succeeded by all of its immediate subordinates, before any other object with the same immediate superior, i.e. in order tree traversal.

3.157	soft line terminator

A line terminator that is allowed to be removed, relocated or replaced in a subsequent layout process.

3.158	spacing ratio

The ratio of line spacing to pel spacing.

3.159	specific layout structure

A set of layout objects and associated content portions.

3.160	specific logical structure

A set of logical objects and associated content portions.

3.161	start-aligned

1)	The result of a layout or imaging process that positions the sequence of character images for a line such that the position point of the first character image of that sequence is positioned on the line home position or at the point specified by the first line indentation or overhang if any.

2)	A tabulation alignment that positions the sequence of character images for a specified character string such that the position point of the first character image of that sequence is positioned at the tabulation stop.

3.162	start edge

The edge of the positioning area of a basic layout object that is in the direction opposite to the character path.

3.163	structural element

The structural elements of a document are the content portion, the object and the object class.

3.164	tabulation alignment

A layout or imaging process that causes the sequence of character images for a specified character string to be positioned according to a specified method, (start-aligned, end-aligned, centred or aligned-around) at a specified point (tabulation stop) along a reference line.

3.165	tabulation stop

A position along a reference line that is to be used for a specified method (start-aligned, end-aligned, centred or aligned-around) of tabulation alignment.

3.166	text unit

A data structure representing a content portion description.

3.167	top edge

The edge of the positioning area of a basic layout object that is in the direction opposite to the line progression.

3.168	top left corner

The corner of a layout object that is least progressed both in the horizontal and vertical directions of this layout object.

3.169	top right corner

The corner of a layout object that is most progressed in the horizontal direction and least progressed in the vertical direction of this layout object.

3.170	trailing edge

The edge of a frame or block that is orthogonal to the direction of the layout path and that is met first, from the outside of the frame or the block, in the direction of the layout path.

3.171	unit scaling

A scaling factor (an integer or a fraction) that is applied to the basic measurement unit (BMU) to derive a scaled measurement unit (SMU).

3.172	variable spacing

The characteristic of a font wherein the distance between the position point and the escapement point for different character images may be different.

3.173	widow

One or more lines of text associated with preceding text but isolated from it by a page or column boundary.