SDPL 2004Notes 4: Intro to Style Sheets1 4. Introduction to Style Sheets n Discussed recently: –Programmatic manipulation of documents n Now a more human point of view: –How to specify the visual representation of structured documents? n Concepts, properties and requirements of style systems on a general level –later examples of concrete style languages (CSS, XSL)

SDPL 2004Notes 4: Intro to Style Sheets2 Introduction to Style Sheets (Inspired by Brüggemann-Klein & Wood: Electronic Style Sheets. Univ. Freiburg, Institut für Informatik, Bericht 43, 1992) n Declarative markup of structured documents indicates only the syntactic structure –no semantics (processing, formatting, …) n Electronic style sheets –specify layout and appearance of document content –e.g., Word styles, or LaTeX style files (macros), FrameMaker templates; CSS and XSL style sheets

SDPL 2004Notes 4: Intro to Style Sheets3 Style Sheets? n (Tyylisivu tai tyylisäännöstö) n In traditional publishing: set of rules about diction and language for some manuscript n Electronic style sheets –deal with graphical layout of documents (In future with aural properties, too?) –setting and changing of properties controlling layout and appearance of document content –define a mapping from documents (structure+content) to external representation on a presentation medium (paper, screen, audio, …)

SDPL 2004Notes 4: Intro to Style Sheets4 Why Style Sheets? n Separation of content and presentation is a basic "dogma" in structured documenting –supports maintenance and multi-use of documents –(unnecessary complication for single-purpose or single-use documents) n Relationship between documents and style sheets is many-to-many –single style for many documents »supports manageability (of, say, consistent look and feel of a corporate Web site) –many styles for a single document »supports multiple output media (print, different Web clients, hand-held-devices, …)

SDPL 2004Notes 4: Intro to Style Sheets5 Tasks of a Style Sheet n Style sheet guides the transformation of –descriptive markup into formatter input (stream of formatting commands and text) »called transcription by Brüggemann-Klein & Wood n “Styling = transforming + formatting” –matches Extensible Stylesheet Language: –XSL = XSLT (transformation language) + XSL FO (formatting language)

SDPL 2004Notes 4: Intro to Style Sheets6 Formatter (muotoilin, muotoiluohjelma) n Formatter is a device (program) capable to format a document (obviously!), which involves –hyphenation (breaking of character sequences) –typeface attribution (characters into glyphs) »e.g, single glyph for " fi" –line breaking (assembling glyphs into lines) –page breaking (grouping lines onto pages) fi

SDPL 2004Notes 4: Intro to Style Sheets7 Process of Transformation (muunnos) Formatter input Transformation TeX FOT (XSL formatting object tree) Style sheet - Latex style file, CSS, XSLT

SDPL 2004Notes 4: Intro to Style Sheets8 Process of Formatting (muotoilu) n Creates a detailed description of presentation –> style sheet may not have complete control of the final formatted presentation!

SDPL 2004Notes 4: Intro to Style Sheets9 Process of Rendering (hahmonnus) n Display/play the document on output medium

SDPL 2004Notes 4: Intro to Style Sheets10 Style Rules n Style sheet is a set of style rules –Attach transformations to document elements n Most style rules in practise structure-based –associated to instances of element types in the document structure tree n Also grammar-based style rules have been studied –associated to occurrences of element types in the document grammar

SDPL 2004Notes 4: Intro to Style Sheets11 Transcription types n Fundamental operations of style rules fall into following transcription types: 1. calls of parameterised formatting tasks 2. generation of text 3. automatic numbering 4. rearrangement of elements n Application of transcriptions can depend on the context the element

SDPL 2004Notes 4: Intro to Style Sheets12 Context Specification (1) n General rule: –semantically equivalent structures (instances of the same element type) should be formatted identically n Exceptions (due to conventions, aesthetics, etc) –all paragraphs indented, except for the first one –headings numbered 1, 2, … in body but A), B), … in appendix –author lists in references: ‘‘ Aho and Ullman ’’ (just a few) vs ‘‘ Aho et al. ’’ (if several authors) –indication of target element type ( Table, Figure, Section,...) for cross references

SDPL 2004Notes 4: Intro to Style Sheets13 Context Specification (2) n Need access to ancestors, siblings, descendants, targets of cross references n Context conditions by a context predicate –Boolean expression built of »a reference to the current element »functions like parent, leftSibling, leftMostSibling, children, and ref –Rule applied if the context condition is true n Context specification orthogonal to transcription types (In XSL through the XPath expression language)

SDPL 2004Notes 4: Intro to Style Sheets14 Parameterised Formatting Tasks n The most common transcription type: n set formatting characteristics for sub-elements –typeface attribution (for strings or inline-elements) –line breaking (for paragraphs or blocks) –page breaking (for documents) –parameterised by type size, line length, indentation, page height… Hierarchy of elements  hierarchy of nested formatting tasks  hierarchy of nested presentation areas Hierarchy of elements  hierarchy of nested formatting tasks  hierarchy of nested presentation areas

SDPL 2004Notes 4: Intro to Style Sheets15 Hierarchy in Formatting Document structure Formatting tasks / presentation areas create pages create block

SDPL 2004Notes 4: Intro to Style Sheets16 Derived or Inserted Content n boilerplate text –text not present in the source document –e.g., letter headings, © marks, bullets, … n textual content inserted at the beginning or at the end of the current element n table of contents, indexes –need to specify the source of included material

SDPL 2004Notes 4: Intro to Style Sheets17 Numbering (1) n Different schemes –consecutively through document »same numbering sequence, possibly common to a set of element types (e.g., for Theorems and Examples) –nested numbering for, say, nested lists »relative to occurrences of another element type higher in document hierarchy

SDPL 2004Notes 4: Intro to Style Sheets18 Numbering (2) Example of different numbering schemes: Section 1 Theorem 1, or 1.1 Figure 2, or 1, or 1.2, or 1.1 Section 2 Theorem 3, or 2, or 2.1 Example of different numbering schemes: Section 1 Theorem 1, or 1.1 Figure 2, or 1, or 1.2, or 1.1 Section 2 Theorem 3, or 2, or 2.1 n often via named counters with a start value and a scope (e.g., in CSS2) –In XSLT: special expressions for generating numbers

SDPL 2004Notes 4: Intro to Style Sheets19 Sub-element Rearrangement n Examples –reverse the order of titles and authors in references –sorting of the reference list »requires functions operating on textual contents n Sub-element suppression a special case n Rearrangement not supported by the weakest style systems (e.g., CSS)

SDPL 2004Notes 4: Intro to Style Sheets20 Viewpoint on Style Languages n Style languages should support traditional stylistic conventions discussed above n Next a look at CSS, and later at XSL –How do the discussed concepts appear in the languages? –How do the languages support these general requirements?