====== Filters. How to modify or format data on rendering. ======

Filters are used to modify or to apply some special formatting rules to variables in [[.expressions|expressions]]. Filters are separated from other  parts of an expression by vertical line. Several filters can be combined into a "pipe":

<code>
{$UserName|trim|capitalize}
</code>

In the example above, //trim// filter first removes spaces from the begin and end of the $UserName variable and then //capitalize// filter converts first letter to uppercase. In the compiled PHP file we will get something like this:

<code php>
 <?php echo ucfirst(trim($UserName)); ?>
</code>

===== Filters parameters =====

Filters may also require additional information called **parameters**. The syntax for specifying parameters is:

<code>
{$UserName|default:"anonymous"}
</code>

If no value is specified for the UserName variable, then the value of "anonymous" is used. A parameter may be either a number constant, a string constant, or a variable.

Multiple parameters can be specified separated by commas:

<code>
{$value|number:2, '. ', ' '}
</code>

Here is an example of using of a variable as a filter parameter:
<code>
<? $size = 10; ?>
<pre>{$PlainText|wordwrap:$size}</pre>
</code>

In most cases {{macro}} filters are just wrappers for PHP function like trim, strtoupper, number_format etc. Default {{macro}} filters can be found in limb/macro/src/filter folder.