# Class Pxp_reader.lookup_system_id_as_string

    class lookup_system_id_as_string : ?fixenc:Pxp_types.encoding -> (string * string) list -> resolver

Looks up resolvers for URL identifiers: The catalog argument specifies pairs `(url, text)` mapping URL's to XML text (which must begin with `<?xml ...?>`).

Note: URL's are simply compared literally, without making relative IDs absolute. See `norm_system_id` below for how to improve this.

`fixenc`: Overrides the encoding of the strings.