KeyAndOperator represents key and operator.

Values represents values.

Lexer represents the Lexer struct for label selector.

ScannedItem contains the Token and the literal produced by the lexer.

Selector represents a label selector.

ByKey sorts requirements by key to obtain deterministic parser.

ParserContext represents context during parsing: some literal for example 'in' and 'notin' can be recognized as operator for example 'x in (a)' but it can be recognized as value for example 'value in (in)'.