useNamedReferences doesn't work for all characters

[carolinex]

While setting useNamedReferences to true and encodeEverything to true, the character / is encoded as / but the character \ is encoded as \ The same happens with the hyphen/minus character, which is encoded as -

var entity = he.encode(html, {
          useNamedReferences: true,
          encodeEverything: true
})