Adds meta information to an already defined item
    of the model being defined.
    @param item_name: name of the model item the meta data should be added to.
    @type item_name: str or unicode
    @param name: name of the meta data class
    @type name: str or unicode
    @param value: metadata value
    @type value: str or unicode
    @param scheme: format information about the value
    @type scheme: str or unicode or None

def item_meta(item_name, name, value, scheme=None):
    """
    Adds meta information to an already defined item
    of the model being defined.
    @param item_name: name of the model item the meta data should be added to.
    @type item_name: str or unicode
    @param name: name of the meta data class
    @type name: str or unicode
    @param value: metadata value
    @type value: str or unicode
    @param scheme: format information about the value
    @type scheme: str or unicode or None
    """
    _annotate("item_meta", item_name, name, value, scheme=scheme)