'Replace the <var> the variable and prefix it with \'A \' or \'a \'
For example the string <var>An(item(1))</var> is converted into just:
A <var>item(1)</var>'

def filter_var(self, match, var_node):

    an_text = (self._an_map[match.group(1).strip()] + '    ')
    prev_node = var_node.getprevious()
    parent_node = var_node.getparent()
    if (prev_node is not None):
        prev_node.tail = ((prev_node.tail or '') + an_text)
    elif (parent_node is not None):
        parent_node.text = ((parent_node.text or '') + an_text)
    var_node.text = match.group(2).strip()
    return True
