nl_tokens: https : // html . spec . whatwg . org / multipage / common - microsyntaxes . html#parse - a - month - string
pl_tokens: function parseMonthString ( str ) { const matches = monthRe . exec ( str ) ; if ( ! matches ) { return null ; } const <mask> = Number ( matches [ 1 ] ) ; if ( year <= 0 ) { return null ; } const month = Number ( matches [ 2 ] ) ; if ( month < 1 || month > 12 ) { return null ; } return { year , month } ; }