# Class Pxp_reader.lookup_id_as_string

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

The list (catalog) argument specifies pairs `(xid,s)` mapping external IDs `xid` to strings `s`. The string 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.