The xhtml form template sets up the wrapping table around all the other xhtml theme form elements. In addition to creating this wrapping table, the opening and closing templates also, if the validate parameter is set to true, enable Pure JavaScript Client Side Validation. See the form.ftl contents:

<#include "/${parameters.templateDir}/xhtml/form-validate.ftl" />
<#include "/${parameters.templateDir}/simple/form.ftl" />
<#include "/${parameters.templateDir}/xhtml/control.ftl" />

The closing template, form-close.ftl:

<#include "/${parameters.templateDir}/xhtml/control-close.ftl" />
<#include "/${parameters.templateDir}/simple/form-close.ftl" />
<#include "/${parameters.templateDir}/xhtml/form-close-validate.ftl" />