Gets the value of an HTTP variable.
HTML_VARIABLE ( var-name [ [ , instance ] , header-field)
var-name The name of the an HTTP variable.
instance If more than one variable has the same name, the instance number of the field instance, or NULL to get the first one. Useful for select lists that permit multiple selections.
header-field In a multipart request, a header field name associated with the named field.
This function returns the value of the named HTTP variable. It is used when processing an HTTP request through a Web service.