typo fixes

    represents.</p>

    <p>The full list of headers recognized is available in the <a

    href="mod/mod_negotiation.html#typemaps">mod_negotation

    href="mod/mod_negotiation.html#typemaps">mod_negotiation

    typemap</a> documentation.</p>

</section>

    major releases (for example, from 1.3 to 2.0 or from 2.0 to 2.2),

    there will likely be major differences in the compile-time and

    run-time configuration that will require manual adjustments.  All

    modules will also need to be upgraded to accomodate changes in the

    modules will also need to be upgraded to accommodate changes in the

    module API.</p>

    <p>Upgrading from one minor version to the next (for example, from

  becomes stale, and the time the stale entity is fully refreshed. On a busy

  server, a significant number of requests might arrive during this time, and

  cause a <strong>thundering herd</strong> of requests to strike the backend

  suddenly and unpredicably.</p>

  suddenly and unpredictably.</p>

  <p>To keep the thundering herd at bay, the <directive>CacheLock</directive>

  directive can be used to define a directory in which locks are created for

  URLs <strong>in flight</strong>. The lock is used as a <strong>hint</strong>

    should be the preferred choice. This is explained further in the <a

    href="../caching.html#inmemory">Caching Guide</a>.  In particular,

    this module's cache is <em>per-process</em>, which can be partially

    mitigated by configuring threaded MPMS to use fewer child processes

    mitigated by configuring threaded MPMs to use fewer child processes

    via configuration of larger values for <directive 

    module="mpm_common">ThreadsPerChild</directive>.  This module's cache is 

    also limited to storing a single variant (see HTTP Vary: header) of each