All methods and properties named like “_{something}” are counted as private and are compressed in webix.js
You can compress webix_debug.js with uglify-js or any other compression tool, so you will have a smaller file where you can use any methods.
Please beware while we maintain backward compatibility of public API, we may change signatures and names of private methods without notice.
On side note, in most cases you need not use private methods to modify behavior of component, all major methods are public and some inner properties has public aliases ( some._viewobj is equal to some.$view, some._settings is equal to some.config ). All extra extensions at webix.com - pivot, kanban, scheduler - are written by using only public API of components.
In future, if such necessity will arise, we can provide a separate build of Webix, that will contain all minifications except of private methods minification