# Class Pxp_reader.lookup_system_id_as_file

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

Looks up resolvers for URL identifiers: The catalog argument specifies pairs `(url, filename)` mapping URL's to filenames. The filenames must already be encoded in the character set the system uses for filenames.

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

`fixenc`: Overrides the encoding of the file contents. By default, the standard rule is applied to find out the encoding of the file.