More specifically, tree-sitter does not handle grammars well where a non-terminal can possible produce the empty word, unless the terminal is the top-level non-terminal. Sometimes it warns of this

• empty_regex_no_warning

Tree-Sitter does not warn when a regex matches the empty string

• regex_empty_rule_warning
• optional_empty_rule_warning

Tree-Sitter does emit a warning when repeat() or optional() is used in a non-top-level rule

There's some odd interactions when repeat / optional are wrapped into token()

• token(repeat(...)) bug [1]
• empty top-level string bug [2]
• token(repeat(...)) / token(optional(...)) bug [3]

[1] tree-sitter/tree-sitter#1271 [2] tree-sitter/tree-sitter#1111 [3] tree-sitter/tree-sitter#1156