It has been possible to save a custom easing in the easing functions menu: you create your own and Add it to List (look at my screenshot)
This 'Add to List' option creates a custom item but it stays available only inside that very document. If you open a new document and want to use your custom function created in a previous doc, it isn't there anymore.
Here comes the Feature Request:
A kind of 'MySnippets-list' for saving fav JS functions in a library within Hype on the program level, so that it will be available in all hype documents, new or previously created.