[office/tellico] doc: Update SRU documentation

[Robby Stephenson]

Git commit 425e46ce304dc87b005be7518187554a52c15b25 by Robby Stephenson.
Committed on 25/07/2025 at 02:09.
Pushed by rstephenson into branch 'master'.

Update SRU documentation

M  +9    -3    doc/configuration.docbook
M  +-    --    doc/sru-options.png
M  +-    --    doc/z3950-options.png

https://invent.kde.org/office/tellico/-/commit/425e46ce304dc87b005be7518187554a52c15b25

diff --git a/doc/configuration.docbook b/doc/configuration.docbook
index bbb9b8805..d000fe42b 100644
--- a/doc/configuration.docbook
+++ b/doc/configuration.docbook
@@ -258,9 +258,15 @@ Some servers require a username and password for access. &appname; can use and s
 <title>SRU Servers</title>
 
 <para>
-SRU stands for <ulink url="http://www.loc.gov/standards/sru/">Search/Retrieve via &URL;</ulink> and is a standard search protocol for
-Internet searches. Some libraries use it for providing access to their data catalogs. Among them, the <ulink url="http://www.loc.gov/z3950/lcserver.html#oppr">US Library of Congress</ulink> is probably
-the best known.
+<acronym>SRU</acronym> stands for <ulink url="http://www.loc.gov/standards/sru/">Search/Retrieve via &URL;</ulink> and is a standard search protocol for
+Internet searches. Some libraries use it for providing access to their data catalogs. Among them, the <ulink url="http://www.loc.gov/z3950/lcserver.html#oppr">US Library of Congress</ulink> is probably the best known.
+</para>
+
+<para>
+Custom fields can be added to tweak Tellico's interaction with the SRU server. To override particular query protocols, use the x-tellico prefix and the desired field name. For
+example, to query ISBN using the bib schema instead of the bath schema, set <userinput>x-tellico-isbn</userinput>=<userinput>bib.isbn</userinput>. &tellico; can also make the
+SRU request by the POST method, if <userinput>x-tellico-method</userinput>=<userinput>POST</userinput>. In order to override the record schema, add a custom field setting
+<userinput>recordSchema</userinput>=<userinput>unimarcXchange</userinput>.
 </para>
 
 <screenshot>
diff --git a/doc/sru-options.png b/doc/sru-options.png
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