mod_speling Attempts to correct mistaken URLs by ignoring capitalization, or attempting to correct various minor misspellings. Extension mod_speling.c speling_module

Requests to documents sometimes cannot be served by the core apache server because the request was misspelled or miscapitalized. This module addresses this problem by trying to find a matching document, even after all other modules gave up. It does its work by comparing each document name in the requested directory against the requested document name without regard to case, and allowing up to one misspelling (character insertion / omission / transposition or wrong character). A list is built with all document names which were matched using this strategy. Erroneous extension can also be fixed by this module.

If, after scanning the directory,

no matching document was found, Apache will proceed as usual and return an error (404 - document not found).
only one document is found that "almost" matches the request, then it is returned in the form of a redirection response (301 - Moved Permanently).
more than one document with a close match was found, then the list of the matches is returned to the client, and the client can select the correct candidate (300 - Multiple Choices).

CheckSpelling Enables the spelling module CheckSpelling on|off CheckSpelling Off server config virtual host directory .htaccess Options

This directive enables or disables the spelling module. When enabled, keep in mind that

the directory scan which is necessary for the spelling correction will have an impact on the server's performance when many spelling corrections have to be performed at the same time.
the document trees should not contain sensitive files which could be matched inadvertently by a spelling "correction".
the module is unable to correct misspelled user names (as in http://my.host/~apahce/), just file names or directory names.
spelling corrections apply strictly to existing files, so a request for the <Location /status> may get incorrectly treated as the negotiated file "/stats.html".

mod_speling should not be enabled in DAV enabled directories, because it will try to "spell fix" newly created resource names against existing filenames, e.g., when trying to upload a new document doc43.html it might redirect to an existing document doc34.html, which is not what was intended.

CheckCaseOnly Limits the action of the speling module to case corrections CheckCaseOnly on|off CheckCaseOnly Off server config virtual host directory .htaccess Options

When set, this directive limits the action of the spelling correction to lower/upper case changes. Other potential corrections are not performed, except when CheckBasenameMatch is also set.

CheckBasenameMatch Also match files with differing file name extensions. CheckBasenameMatch on|off CheckBasenameMatch On server config virtual host directory .htaccess Options

When set, this directive extends the action of the spelling correction to the file name extension. For example a file foo.gif will match a request for foo or foo.jpg. This can be particulary useful in conjunction with MultiViews.