ISO 8601 Durations

dur.go

const (
    decPart = `\d*[.,]\d*`
    intPart = `\d+`

    decS = `(?:(?P<decS>` + decPart + `)S)`
    intS = `(?:(?P<intS>` + intPart + `)S)?`
    sPat = `(?:` + decS + `|` + intS + `)`

    decMin = `(?:(?P<decMin>` + decPart + `)M)`
    intMin = `(?:(?P<intMin>` + intPart + `)M)?`
    minPat = `(?:` + decMin + `|(?:` + intMin + sPat + `))`

    decH = `(?:(?P<decH>` + decPart + `)H)`
    intH = `(?:(?P<intH>` + intPart + `)H)?`
    hPat = `(?:T(?:` + decH + `|(?:` + intH + minPat + `)))?`

    decD = `(?:(?P<decD>` + decPart + `)D)`
    intD = `(?:(?P<intD>` + intPart + `)D)?`
    dPat = `(?:` + decD + `|(?:` + intD + hPat + `))`

    decW = `(?:(?P<decW>` + decPart + `)W)`
    intW = `(?:(?P<intW>` + intPart + `)W)?`
    wPat = `(?:` + decW + `|(?:` + intW + dPat + `))`

    decMon = `(?:(?P<decMon>` + decPart + `)M)`
    intMon = `(?:(?P<intMon>` + intPart + `)M)?`
    monPat = `(?:` + decMon + `|(?:` + intMon + wPat + `))`

    decY = `(?:(?P<decY>` + decPart + `)Y)`
    intY = `(?:(?P<intY>` + intPart + `)Y)?`
    yPat = `(?:` + decY + `|(?:` + intY + monPat + `))`

    durPat = `^P` + yPat + `$`
)

some experimentation