A tree-sitter grammar for Invisible XML

This is an attempt to craft a tree-sitter grammar for Invisible XML. The primary motivation is to get correct syntax highlighting in editors that support tree-sitter.

I know very little about tree-sitter so take everything you find in here with a grain of salt.

Deviations from iXML

The constraints of a tree-sitter grammar differ from the constraints of iXML. Some things that are easy in iXML are difficult or impossible in tree-sitter grammars.

Consequently, this grammar isn’t “the same” as iXML, though it’s expected to be close enough for useful syntax directed highlighting.

This grammar differs from iXML in a number of ways.

1. A tree-sitter grammar can’t have a nonterminal that matches nothing. To address this limitation, an alt has been defined so that it must contain at least one term. In the places where alt appears, it has been made optional.

2. The definition of a set in iXML includes both string and range and range begins with character. A string containing a single character and a character are indistinguishable. This leads to confusion about what ["L"] means (it’s either a string or a broken range). To work around this problem, the tree-sitter grammar defines set a little differently.

3. To support syntax highlighting, one of the goals of this grammar is to expose parts of the syntax that aren’t actually relevant to the grammar (the hyphens in ranges, the parenthesis around alts, etc.).

Emacs mode

The ixml-ts-mode supports tree-sitter based syntax highlighting in Emacs 29.1 assuming you have all the basics covered.