Syntax

There are exactly ten supported forms.

Form	Writes	Index entry
[term]{.index}	term	term
[term]{.index entry="Entry"}	term	Entry
[term]{.index entry="Top!Sub"}	term	Top → Sub
[]{.index entry="Entry"}	nothing	Entry
[term]{.index see="Other"}	term	term, see Other
[term]{.index see-also="Other"}	term	term, see also Other
[term]{.index mention="principal"}	term	term, its locator emphasized
[term]{.index range="open"}	term	term, one locator spanning to its closing mark
[term]{.index range="close"}	term	nothing of its own; it closes the range
[term]{.index index="authors"}	term	term, in the index named authors

The visible text is always left exactly as written. The first form indexes a term under its own text; the second indexes it under something else; the third nests it under a parent heading; the fourth adds an entry with no visible mark on the page. The next two point the reader at a different entry instead of at a page. The seventh says which of a term’s mentions is its principal one. The eighth and ninth mark where a discussion begins and where it ends, so the index prints one locator spanning them rather than a locator at each. The tenth says which of a document’s declared indexes the mark belongs to.

A mark can sit in a figure caption or in an image’s alt text. A mark in a figure caption files one locator, whether or not the figure has an id, and a range can open there. A mark in an image’s alt text files its locator at the image: in HTML and EPUB the locator links to the place just after the image, and in PDF and Typst it prints the image’s page. The alt text itself is left as written.

The forms have a page each: sub-entry levels, cross-references, special characters, terms outside Latin-1, sorting an entry under something else, the principal mention of a term, a discussion that spans pages, placing the index and named indexes.