function name[ $first_var=...; $more_vars=... ; $last_var=...]
... ... ...
endfunction
call name[ $first_var=...; $more_vars=... ; $last_var=...]
functions can also be called from html
<xt:call function="name" first_var="..." more_vars="..." last_var="..."/>
or like this
<xt:call function="name" args="$first_var=...;$more_vars=...;$last_var=..." />