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what is a language''?

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Sun, 2 Mar 1997 18:57:28 +0100

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 i guess that the section heading below is anything else than correct :-) but i do want to share some thoughts and comments i wrote during the day on that topic and the hope that you can help with further thoughts/agreement/disagreement etc frank -------------------------- \section{Clarifying the term language'' within \LaTeX{}}  Within structured documents each portion of the document is explicitly or implicitly labeled with a language tag'' denoting that this portion of the document contains data written in a certain language''. They have the following properties: \begin{itemize} \item   They impose a tree structure on the document. \item   At any one point in the document the current language'' can be   determined. \end{itemize} \TeX{} provides a very special type of region which can be regarded as a language in its own right: mathematical formulas. Although it doesn't follow exactly the same markup convention and doesn't employ the same implementation concepts (as it has built in support for various features) it nevertheless is on an abstract level comparable in most respects. Traditionally these language tags can have two independent semantics: \begin{itemize} \item   Denoting the input conventions used within this region. \item   Denoting the rendering conventions used when formatting this region. \end{itemize} \subsection{Input conventions} There are a number of implicit input conventions employed within a \TeX{} based system, for example, each input character is attached a so called category code that determines certain semantics of that character. A category code of type letter'' or type other'' means that in most situations\footnote{As \TeX{} is a macro language it is of course possible that due to expansion of macros the interpretation of the input is temporarily or even permanently modified.} the character is rendered as a glyph in the slot position corresponding to the \textsc{ascii} code value of the character in the current font. In most cases this means that if, say, the character a' is entered it will eventually result in the glyph a' in the current font. However, one has to be aware that this crucially depends on the font encoding in use. From this observation it follows that for characters of this category type either all font encodings have to produce the same logical glyph or the correspondence between input and output representation have to be explicitly marked up to allow the formatting process to select fonts with the correct font encoding. Another area of input conventions commonly used for language support are the shortrefs, see~\ref{sec:shortrefs}. \subsection{Rendering conventions} There are many rendering conventions that depend or can depend on the language of a textual region. Examples are the hyphenation algorithm employed, the production of fixed strings, typographical conventions, etc. These conventions range from those that most likely need changing when switching from one language to another to those that can be considered being a matter of style but that do not produce incorrect results. For most, if not for all rendering conventions this is a somewhat flexible classification that does depend on various factors and might be different for different applications. \subsection{Discussion} For both types of input conventions it seems that that they are not necessarily tightly bound to the language of a region. For example, it is perfectly possible (although currently not fully supported by \LaTeX{}) to input text in a given language using more than one font encoding and consequently needing different input conventions within the area denoted by a language tag. Similarly the shortrefs have an application range that is not directly linked to language boundaries, see section~\ref{sec:shortref-discussion} for further discussion. Not all decisions the formatter has to make when encountering a language tag (i.e., a change in languages) can be considered as being globally bound to such a border, in fact most of them depend on the current nesting structure, e.g., embedded language fragments might be handled differently then a document with this language as the main language. This is not to say that that there can't be a global bound but that one needs specification flexibility in deciding which conventions are applied/changed at what level.