Parser.AttributesHelpers for getting attribute values
get name attributes returns the attribute value for name in attributes.
get_exn name attributes returns the attribute value for name in attributes.
val optional : Xmlm.name -> Xmlm.attribute list -> string option toptional name attributes returns a parser that returns the attribute value for name in attributes.
val required : Xmlm.name -> Xmlm.attribute list -> string trequired name attributes returns a parser that returns the attribute value for name in attributes and fails if the attribute is not present.