You have probably come here from a link on a protected page. Depending on its level of protection, editing on the page has been wiki sandbox.
For more information on who protected the page and for what reason, please see:
Most pages on Joomla! Documentation are only protected temporarily, to prevent edit wars or to control vandalism. You should be able to edit the page when it is unprotected in a short while. In the meantime, please feel free to discuss the changes you want to make on the talk page of the page in question. However a few types of pages are protected indefinitely:
If you discover a page that appears to have been protected and then forgotten about, you can request to have it unprotected by posting on Project:Requests for page protection. If a page has only recently been protected, it may be best to wait a few days first, unless some resolution has been reached on the talk page.
If you think that an edit needs to be made to a protected page, please discuss the change first on its consensus.