Text Filter Suite

The Text Filter Suite ("TFS", hereafter) is a WordPress plugin which adds some new text filtering functions. In a sense, the core TFS functions could be considered a "meta filter", because they actually provide a framework that let you construct new filters fairly easily. They also provide an easy way to apply filters to post content and comments on a per-post basis. Huh? Can you repeat that in English? Okay, let's try a real-world example. A common feature on many web sites is the automatic handling of acronyms. You'll often see an acronym such as "XHTML" displayed in an alternate style, and when you hover your mouse pointer over it, you get a tool-tip which displays the definition ("eXtended HyperText Markup Language", in this case). You don't want to have to type in the markup for this every time you post something, and automation is what computers are for, right? So, there are several plugins available to handle this sort of automated text subsitution. TFS comes with the "TFS Acronymit" plugin to perform this function. It's based on Matt Mullenweg's original "Acronymit" function, but with a couple of improvements. In Matt's original function, you had to keep the acronym list sorted, longest-to-shortest, and it could get confused by recursive acronyms like 'PHP' ("PHP Hyptertext Processor") or GNU ("GNU's Not Unix"). TFS Acronymit does not have those restrictions. For those who think that expansion of technical acronyms is "teh sux0r" (i.e. "boring"), TFS comes with a variety of more entertaining filters. The current set includes "chef", "fudd", "jive", "kraut", "pirate", and of course, the aforementioned "acronymit". As a word of caution, the "jive" and "kraut" filters are not what you would call "politically correct".

Technically, all you need to do is copy the "text-filter-suite" folder into your "wp-content/plugins" directory, then activate the "TFS Core" plugin from the WordPress admin interface. But, more generally, you'll probably want some of the other filter files, as well. The easiest thing to do will be to just copy all of the ".php" files to your plugins directory, and only activate the ones that interest you. But you can omit any of the "tfs-whatever.php" files (other than tfs-core) that don't interest you. Using the filters Generally, you'll probably want to activate a filter just for specific posts. You do this by adding special "post custom fields" in the "Write Post" form. Custom fields are composed of two parts: the "key" and the "value". The two special keys that activate TFS are "post_filter" and "comment_filter". In either case, the value should be the short name of the TFS filter you wish to apply, e.g. "pirate" or "fudd" (without the quotation marks). Setting the "post_filter" key will apply the filter to the main post text. Setting the "comment_filter" key will apply the filter to the text of all comments on the post. Technical mumbo-jumbo There are only two core TFS functions, plus two more to support the per-post content and comment filtering based on post custom fields. The main entry point is the "filter_cdata_content" function. A TFS filter will call filter_cdata_content, passing the content and the name of a second function. The magic of filter_cdata_content() is that it will only mangle regular text, leaving HTML tags alone. It will automatically call out to the named function, passing it each chunk of non-HTML-tag text (AKA "CDATA", or "Character Data", in XML parlance) in turn. The other core function is "array_apply_regexp". This support function isn't required for every filter, but it is at the core of the included TFS filters, such as the "pirate" filter. It accepts an associative array of regular expressions and replacements, and the content to be filtered. Examine the source of the "chef" and "fudd" filters for some simple examples. The per-post support functions are "tfs_content_filter" and "tfs_comment_filter". These functions are automatically applied to each post and its contents. They look for the "content_filter" and "comment_filter" post custom fields, and apply the appropriate filter functions if they are found.

By default, if the "TFS Pirate" filter is active, it will automatically apply itself to all content on Talk Like a Pirate Day (September 19). If you do not want this filter to automatically activate, set the value of the "$talk_like_a_pirate" variable at the top of the plugin source to "false". The "TFS Acronymit" filter is automatically applied to all posts whenever it is active. You do not need to set special post custom fields in order to use it. Just activate the plugin, and you're ready. To modify which acronyms are defined, see the list at the beginning of the plugin, and modify it as you like, following the format you see there. It is possible to use the TFS core without activating any additional plugins. You can do this with any built-in PHP function accepts a single string as a parameter and returns a string. For example, you could set a post custom "content_filter" with the value "strrev", and the contents of the post would be displayed backwards, or with a value of "strtoupper" to convert the content to all uppercase text. You can only specify a single function in each post custom field. However, you can chain multiple functions together by using the key more than once. For instance, if you wanted all comments for a post to display in uppercase Elmer Fudd text, you would set two post custom fields: comment_filter = strtoupper comment_filter = fudd HOWEVER, note that using PHP built-in functions in this way will bypass the power of the filter_cdata_content() function, which means that it can and will mangle your HTML tags, possibly rendering them useless. For example, applying the strrev function to the string " " will transform it into ">p<", which will confuse your browser in new and wonderful ways. NOTE: These filters can be very CPU intensive. For one thing, they make extensive use of regular expressions, which can be expensive on their own. And for another, they break your content into many small chunks, in order to separate the filterable text from the HTML code, and the filters run separately on each text chunk found. This probably won't be a problem in most cases. But if you have long posts being filtered, and you get a lot of traffic, it could start to add up. A caching plugin (e.g., WP Super Cache, or W3 Total Cache) would probably help in that case.

1.4 - 2015-06-03

• Added '?filter=foo' URL option back in, with a whitelist of allowed functions.

1.3 - 2012-09-18

• Fixed PHP opening shorttag in tfs-acroymit.php
• Eliminated PHP warnings in debug mode
• Removed all closing ?> php tags per WP standards
• Killed generic 'filter' $_REQUEST variable checking

1.2 - 2010-12-10

• Added this changelog to the readme
• Moved the is_feed() handling into the init, to avoid breaking in WordPress 3.1.
• Added notes about the filters being CPU intensive.