The DirectoryIndex directive sets the list of resources to look for, when the client requests an index of the directory by specifying a / at the end of the directory name. Local-url is the (%-encoded) URL of a document on the server relative to the requested directory; it is usually the name of a file in the directory. Several URLs may be given, in which case the server will return the first one that it finds. If none of the resources exist and the Indexes option is set, the server will generate its own listing of the directory.
Example
DirectoryIndex index.html
then a request for http://example.com/docs/ would return http://example.com/docs/index.html if it exists, or would list the directory if it did not.
Fonte: https://httpd.apache.org/docs/2.4/mod/mod_dir.html
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