Parameter “httpencode” defines that value of corresponding variable or result of function will be HTTP-encoded. Data must be sent over the Internet using the ASCII-characters set. It is always possible to have there some non-accessible characters that must be converted into valid ASCII-format.

If you're interest learn more reading http://www.w3schools.com/tags/ref_urlencode.asp.

NOTE: By default the resulting content will be parsed (all <#..> tags will be evaluated) before to apply this filter. You can control this behavior throught the parameter AnalyzeTagParams

<#UserName SetValue="John Smith">
<#UserName httpencode="1">

Output:

John%20Smith