Ambiguity

A grammar is validated on load. An invalid grammar exits 1 with one error and lints nothing.

An optional slot does not separate its neighbours: the slots on either side are checked against each other too.

Malformed slots

Error	Cause
slot `x` needs exactly one of `kind`, `delimiters` or `one-of`	None of them, or more than one
slot `separator` is a `symbol`, so it cannot match `::`	A spelling the kind cannot match
`gap` does not apply to slot `emoji`	A misplaced key on a `one-of`

Error	Cause	Resolution
`a` takes the whole run, leaving nothing for `b`	A `word`, or unrestricted `symbols`, followed by the same kind	A symbol or delimited slot between them
`a` and `b` both start with `x`	Neighbouring spellings share a prefix	Distinct first characters
`b` takes anything, `a`'s spellings included	A closed set before an unrestricted slot of the same alphabet	Close the second slot's `values`
`a` and `b` carry the same delimiters	Two delimited slots with the same pair, at any distance	A different pair; a shared opener alone is allowed
`a` and `b` can start on the same input	Overlapping `one-of` options	Close or separate the options
`a` is optional after a gap, so it can take the start of the description	An optional `word` or unrestricted `symbols` slot after a `gap`	`required = true`, or a delimited slot

word is one alphabet; symbols and symbol share the other.

Run

[[commit.slots]]
name = "type"
kind = "word"

[[commit.slots]]
name = "subtype"
kind = "word"

Shared prefix

[[commit.slots]]
name = "modifiers"
kind = "symbols"
values = ["!", ":"]

[[commit.slots]]
name = "separator"
kind = "symbol"
values = [":"]

Shadowed

[[commit.slots]]
name = "modifiers"
kind = "symbols"
values = ["!"]

[[commit.slots]]
name = "separator"
kind = "symbol"

Same delimiters

[[commit.slots]]
name = "scope"
delimiters = ["(", ")"]

[[commit.slots]]
name = "ticket"
delimiters = ["(", ")"]

Optional after a gap

[[commit.slots]]
name = "emoji"
kind = "symbols"
values = ["✨"]
required = true
gap = true

[[commit.slots]]
name = "keywords"
kind = "word"