+ Multiple database elements defining the names of the accepted
+ databases are allowed in the configuration file. Each
+ of them must contain their own explain record, or must be empty.
+ Notice that explain
+ records come in SRU and Z39.50 flavors, and this filter requires
+ the SRU version. See the
+ <ulink url="&url.zeerex.explain;">ZeeReX Explain</ulink>
+ standard pages and the
+ <ulink url="&url.sru.explain;">SRU Explain</ulink> pages
+ for more information.
+ </para>
+ <para>
+ All Z39.50 packages and all HTTP packages that do not resolve to
+ one configured database name are passed unaltered to the next
+ filters on the route.
+ </para>
+ <para>
+ The SRU <literal>explain</literal> operation is supported,
+ returning either the absolute minimum required by the standard, or
+ a full pre-defined ZeeReX explain record.
+ </para>
+ <para>
+ It supports the SRU <literal>searchRetrieve</literal> operation, which