Better name for important field

It seems to me that when plugins cohabitate with p-tile-skin, there are two pieces of dom they would want to access:  the dom of the "main" part of the tile (which is invisible until the tile is opened---the children appear in it) and the "header" part of the tile.  As far as I can tell, the field in this pull request is the way the plugin would interact with the latter.  As such, it demands a simpler name due to its potential to be used very often.