in match/matchers.go [237:244]
func (m *emptyWhiteStringMatcher) Match(bs []byte) bool {
for _, r := range bytesToString(bs) {
if !(r == 0x9 || r == 0xa || r == 0xc || r == 0xd || r == 0x20 || r == '\t') {
return false
}
}
return true
}