# Class Pxp_reader.lookup_id_as_file

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

The list (catalog) argument specifies pairs `(xid,file)` mapping external IDs `xid` to files. The file is read if an entity with the corresponding `xid` is to be opened.

Note: `SYSTEM` IDs are simply compared literally by this class, without making relative IDs absolute. See `norm_system_id` below for how to improve this.

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