Validates the *form* only of the specified variable.

def _validate_var(self, var):
        """Validates the *form* only of the specified variable."""
        if "/" in var:
            filt, rest = var.split("/")
            if "|" in rest:
                varname, prop = rest.split("|")
                return prop != ""
            elif rest == "timing":
                return True
            else:
                return False
        else:
            return True