improve comment in html_diff_navigation

diff of removed page, require handling right rev=0

When page is removed, and diff can be requested between a revision and
current situation. This results in right revision is 0.

Similar case just a

diff of removed page, require handling right rev=0

When page is removed, and diff can be requested between a revision and
current situation. This results in right revision is 0.

Similar case just after creating a page. A diff between the first
version and nothing before, result in left revision is 0.

In these cases a empty dummy revision is placed as selected value in
dropdown. Otherwise user got distracted by the revisions details shown
in select field, which are not related to the diff below.

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improved positioning of diff options

Check if revision is defined at all before comparing

extract navigation html to separated method

Fix PHPDocs emailadressvalidator

PHPDocs form

Improve PHPDocs pageutils

PHPDocs of cache classes

PHPDocs for Doku_Event and handler

cleanup PHPDocs: DokuWiki_Syntax_Plugin is a DokuWiki_Plugin as well

fix last merge

add visibility keywords and PHPDocs for cache

remove '' from list, its not part of the hook array

fix httputils PHPDocs

Add dynamic declared _time attribute to cache object

PHPDocs improvements and minor fixes feedcreator

Improve PHPDocs, rename auth_basic to DokuWiki_Auth_Plugin

PHPDocs internallink

Improve PHPDocs html.php

Reorganise generation and displaying of html. Added comments

Put diff navigation in diff view table

Code reformatting html_diff

roughly styled diff nav row

remove unnecessary strings and Dutch diff strings (better later once)