This file is indexed.

/var/lib/xkb/README.compiled is in xserver-common 2:1.15.1-0ubuntu2.

This file is owned by root:root, with mode 0o644.

The actual contents of the file can be viewed below.

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The X server uses this directory to store the compiled version of the
current keymap and/or any scratch keymaps used by clients.  The X server
or some other tool might destroy or replace the files in this directory,
so it is not a safe place to store compiled keymaps for long periods of
time.  The default keymap for any server is usually stored in:
     server-<SHA1>.xkm

where <SHA1> is the SHA1 hash of keymap source, so that compiled
keymap of different keymap sources are stored in different files.

Unless the X server is modified, sharing this directory between servers on
different hosts could cause problems.