Yet another split thread

I know everyone is probably pretty tired of answering questions about splits, but here goes: When watching some of the aerial silk stuff and some acrobatics stuff, I see people doing a full front split with double footlocks or a partner is holding her over his head in a front split where it seems that the person doing the split is holding her full weight with her split. My question is: how can you work up to that? Obviously having a flat floor split is a prerequisite, but is it a matter of strength as well as flexibility? Is there some sort of leverage trick? Thanks one and all for indulging my curiosity.