LaTeX3 Programming Conventions

Release 2024-12-09

Overview

The files of the l3kernel bundle provide an API for TeX programmers with defined syntax conventions, completely separating it from document level syntax. Hence, the commands provided are not intended for use at the document level nor for use in describing design layouts in document class files.

This API provides the foundation on which new additions to the LaTeX kernel and other advanced extensions are built. The programming layer is designed to be loaded as part of LaTeX2ε format building or as a loaded package with plain TeX or other formats.

The syntax and functionality provided by l3kernel is regarded by the LaTeX team as stable. There may still be changes to some functions, but these will be very minor when compared to the scope of l3kernel. In particular, no functions will be removed, although some may be deprecated.

Requirements

The l3kernel bundle requires the ε-TeX extensions and a number of additional 'utility' primitives, almost all of which were first added to pdfTeX. In particular, the functionality equivalent to the following pdfTeX primitives must be available

• \ifincsname
• \ifpdfprimitive
• \pdfcreationdate
• \pdfelapsedtime
• \pdffiledump
• \pdffilemoddate
• \pdffilesize
• \pdflastxpos
• \pdflastypos
• \pdfmdfivesum
• \pdfnormaldeviate
• \pdfpageheight
• \pdfpagewidth
• \pdfprimitive
• \pdfrandomseed
• \pdfresettimer
• \pdfsavepos
• \pdfsetrandomseed
• \pdfshellescape
• \pdfstrcmp
• \pdfuniformdeviate

For ease of reference, these primitives will be referred to as the 'pdfTeX utilities'. With the exception of \expanded, these have been present in pdfTeX since the release of version 1.40.0 in 2007; \expanded was added for TeX Live 2019. Similarly, the full set of these utility primitives has been available in XeTeX from the 2019 TeX Live release, and has always been available in LuaTeX (some by Lua emulation). The Japanese pTeX and upTeX gained all of the above (except \ifincsname) for TeX Live 2019 and \ifincsname for TeX Live 2020.

Starting from release 2023-05-15, the \expanded primitive is required. Its slow emulation has been removed.

In addition to the above, engines which are fully Unicode-compatible must provide the functionality of the following primitives, documented in the LuaTeX manual

• \Uchar
• \Ucharcat
• \Umathcode

The existence of the primitive \Umathcode is used as the marker for Unicode support.

Issues

The issue tracker for LaTeX3 is currently located on GitHub.

The LaTeX Project

Development of LaTeX3 is carried out by The LaTeX Project.

The development team can be contacted by e-mail: <latex-team@latex-project.org>.

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