def add_sibling(self, sibling):
assert self.is_pseudo is False<EOL>if self.siblings is None:<EOL><INDENT>self.siblings = list()<EOL>self.multi_rep = self<EOL><DEDENT>sibling.multi_rep = self<EOL>self.siblings.append(sibling)<EOL>
Designate this a multi-feature representative and add a co-feature.

Some features exist discontinuously on the sequence, and therefore
cannot be declared with a single GFF3 entry (which can encode only a
single interval). The canonical encoding for these types of features is
called a multi-feature, in which a single feature is declared on
multiple lines with multiple entries all sharing the same feature type
and ID attribute. This is commonly done with coding sequence (CDS)
features.

In this package, each multi-feature has a single "representative"
feature object, and all other objects/entries associated with that
multi-feature are attached to it as "siblings".

Invoking this method will designate the calling feature as the
multi-feature representative and add the argument as a sibling.