The attribute to set or unset is specified by attribute. This
can be one of the standard attribute names G_MENU_ATTRIBUTE_LABEL,
G_MENU_ATTRIBUTE_ACTION, G_MENU_ATTRIBUTE_TARGET, or a custom
attribute name.
Attribute names are restricted to lowercase characters, numbers
and '-'. Furthermore, the names must begin with a lowercase character,
must not end with a '-', and must not contain consecutive dashes.
must consist only of lowercase
ASCII characters, digits and '-'.
If value is non-null then it is used as the new value for the
attribute. If value is null then the attribute is unset. If
the value #GVariant is floating, it is consumed.
Sets or unsets an attribute on menu_item.
The attribute to set or unset is specified by attribute. This can be one of the standard attribute names G_MENU_ATTRIBUTE_LABEL, G_MENU_ATTRIBUTE_ACTION, G_MENU_ATTRIBUTE_TARGET, or a custom attribute name. Attribute names are restricted to lowercase characters, numbers and '-'. Furthermore, the names must begin with a lowercase character, must not end with a '-', and must not contain consecutive dashes.
must consist only of lowercase ASCII characters, digits and '-'.
If value is non-null then it is used as the new value for the attribute. If value is null then the attribute is unset. If the value #GVariant is floating, it is consumed.
See also gio.menu_item.MenuItem.setAttribute for a more convenient way to do the same.