go/src/net/http/internal/ascii/print.go

// EqualFold is [strings.EqualFold], ASCII only. It reports whether s and t
// are equal, ASCII-case-insensitively.
func EqualFold(s, t string) bool { … }

// lower returns the ASCII lowercase version of b.
func lower(b byte) byte { … }

// IsPrint returns whether s is ASCII and printable according to
// https://tools.ietf.org/html/rfc20#section-4.2.
func IsPrint(s string) bool { … }

// Is returns whether s is ASCII.
func Is(s string) bool { … }

// ToLower returns the lowercase version of s if s is ASCII and printable.
func ToLower(s string) (lower string, ok bool) { … }