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Historical perspective on RTE transformations¶
The next sections describe in more details the necessity of RTE transformations. The text was written at the birth of transformations and might therefore be somewhat old-fashioned. However it checked out generally OK and may help you to further understand why these issues exist. The argumentation is still valid.
Properties and transformations¶
The RTE applications typically expect to be fed with content formatted as HTML. In effect an RTE will discard content it doesn't like, for instance fictitious HTML tags and line breaks. Also the HTML content created by the RTE editor is not necessarily as 'clean' as you might like.
The editor has the ability to paste in formatted content copied/cut from other websites (in which case images are included!) or from text processing applications like MS Word or Star Office. This is a great feature and may solve the issue of transferring formatted content from e.g. Word into TYPO3.
However these inherent features - good or bad - raises the issue how to handle content in a field which we do not wish to 'pollute' with unnecessary HTML-junk. One perspective is the fact that we might like to edit the content with Netscape later (for which the RTE cannot be used, see above) and therefore would like it to be 'human readable'. Another perspective is if we might like to use only Bold and Italics but not the alignment options. Although you can configure the editor to display only the bold and italics buttons, this does not prevent users from pasting in HTML-content copied from other websites or from Microsoft Word which does contain tables, images, headlines etc.
The answer to this problem is a so called 'transformation' which you can configure in the $TCA (global, authoritative configuration) and which you may further customize through Page TSconfig (local configuration for specific branches of the website). The issue of transformations is best explained by the following example from the table, tt_content (the content elements).
RTE transformations in Content Elements¶
The RTE is used in the bodytext field of the content elements, configured for the types "Text" and "Text & Images".
The configuration of the two 'Text'-types are the same: The toolbar includes only a subset of the total available buttons. The reason is that the text content of these types, 'Text' and 'Text & Images' is traditionally not meant to be filled up with HTML-codes. But more important is the fact that the content is usually (by the standard TypoScript content rendering used on the vast majority of TYPO3 websites!) parsed through a number of routines.
In order to understand this, here is an outline of what typically happens with the content of the two Text-types when rendered by TypoScript for frontend display:
All line breaks are converted to
(Doing this enables us to edit the text in the field rather naturally in the backend because line breaks in the edit field comes out as line breaks on the page!)
All instances of 'http://...' and 'mailto:....' are converted to links.
(This is a quick way to insert links to URLs and email address)
The text is parsed for special tags, so called 'typotags', configured in TypoScript. The default typotags tags are
<TYPOHEAD>(making headlines) and
<TYPOCODE>(making monospaced formatting).
<LINK>tag is used to create links between pages inside TYPO3. Target and additional parameters are automatically added which makes it a very easy way to make sure, links are correct.
<TYPOLIST>renders each line between the start and end tag as a line in a bulletlist, formatted like the content element type 'Bulletlist' would be. This would typically result in a bulletlist placed in a table and not using the bullet-list tags from HTML.
<TYPOHEAD>would display the tag content as a headline. The type-parameter allows to select between the five default layout types of content element headlines. This might include graphical headers.
<TYPOCODE>is not converted).
All other 'tags' found in the content are converted to regular text (with htmlspecialchars) unless the tag is found in the 'allowTags' list.
(This list includes tags like 'b' (bold) and 'i' (italics) and so these tags may be used and will be outputted. However tags like 'table', 'tr' and 'td' is not in this list by default, so table-html code inserted will be outputted as text and not as a table!)
Constants and search-words - if set - will be highlighted or inserted.
(This feature will mark up any found search words on the pages if the page is linked to from a search result page.)
And finally the result of this processing may be wrapped in
<p>-tags or whatever is configured. This depends on whether a stylesheet is used or not. If a stylesheet is used the individual sections between the typotags are usually wrapped separately.
Now lets see how this behaviour challenges the use of the RTE. This describes how the situation is handled regarding the two Text-types as mentioned above. (Numbers refer to the previous bulletlist):
Line breaks: The RTE removes all line breaks and makes line breaks itself by either inserting a
<DIV>...</DIV>. This means we'll have to convert existing lines to
<P>...</P>before passing the content to the RTE and further we need to revert the
<P>sections in addition to the
<BR>-tagsto line breaks when the content is returned to the database from the RTE.
The greatest challenge here is however what to do if a
<P>tag has parameters like 'class' or 'align'. In that case we can't just discard the tag. So the tag is preserved.
The substitution of http:// and mailto: does not represent any problems here.
"Typotags": The typotags are not real HTML tags so they would be removed by the RTE. Therefore those tags must be converted into something else. This is actually an opportunity and the solution to the problem is that all
<LINK>-tags are converted into regular
<TYPOLIST>tags are converted into
<UL>sections (ordered/unordered lists, type depends on the type set for the
<TYPOHEAD>-tags are converted to <Hx> tags where the number is determined by the type-parameter set for the
<TYPOHEAD>-tag. The align/class-parameter - if set - is also preserved. When the HTML- tags are returned to the database they need to be reverted to the specific typotags.
Other typotags (non-standard) can be preserved by being converted to a
<SPAN>-section and back. This must be configured through Page TSconfig.
(Update: With "css_styled_content" and the transformation "ts_css" only the
<link>typotag is left. The
<typohead>tags are obsolete and regular HTML is used instead)
Allowed tags: As not all tags are allowed in the display on the webpage, the RTE should also reflect this situation. The greatest problem is tables which are (currently) not allowed with the Text- types. The reason for this goes back to the philosophy that the field content should be human readable and tables are not very 'readable'.
(Update: With "css_styled_content" and the transformation "ts_css" tables are allowed)
Constants and search words are no problem.
Global wrapping does not represent a problem either. But this issue is related more closely to the line break-issue in bullet 1.
Finally images inserted are processed very intelligently because the 'magic' type images are automatically post-processed to the correct size and proportions after being changed by the RTE in size.
Also if images are inserted by a copy/paste operation from another website, the image inserted will be automatically transferred to the server when saved.
In addition all URLs for images and links are inserted as absolute URLs and must be converted to relative URLs if they are within the current domain.
These actions are done by so called transformations which are
configured in the
$TCA. Basically these transformations are admittedly
very customized to the default behavior of the TYPO3 frontend. And
they are by nature "fragile" constructions because the content is
transformed back and forth for each interaction between the RTE and
the database and may so be erroneously processed. However they serve
to keep the content stored in the database 'clean' and human readable
so it may continuously be edited by non-RTE browsers and users. And
furthermore it allows us to insert TYPO3-bulletlists and headers
(especially graphical headers) visually by the editor while still
having TYPO3 controlling the output.