The Style Guide has recently been rewritten. Please take a moment to review the new guidelines.
Has subobject"Has subobject" is a predefined property representing a <a rel="nofollow" class="external text" href="https://www.semantic-mediawiki.org/wiki/Help:Container">container</a> construct and is provided by <a rel="nofollow" class="external text" href="https://www.semantic-mediawiki.org/wiki/Help:Special_properties">Semantic MediaWiki</a>.