Create is the CMS UI shell around a WYSIWYG editor (well, potentially around other widgets you need like datepickers and choosers as well). We could use Mercury quite easily as another editor option.

Create's editor options are provided as jQuery UI wrapper widgets, for example: https://github.com/bergie/create/blob/master/src/editingWidg...

BTW, check out http://blog.liip.ch/archive/2012/03/20/cmf-editor-overview-s... and http://iks.alkacon.com/en/ if you want to see a bit more comprehensive Create UI setups.