nl_tokens: https : // html . spec . whatwg . org / multipage / common - microsyntaxes . html#parse - a - yearless - date - string
pl_tokens: function parseYearlessDateString ( str ) { const matches = yearlessDateRe . exec ( str ) ; if ( ! matches ) { return null ; } const month = Number ( matches [ 1 ] ) ; if ( month < 1 || month > 12 ) { return null ; } const day = Number ( matches [ 2 ] ) ; if ( day < 1 || day > numberOfDaysInMonthOfYear ( month , 4 ) ) { return null ; } return { month , <mask> } ; }