Libgdx - Why is Bullet and FreeType is not compatible with HTML?

I have attempted to do the following

Generator Configuration

When I tried to check either Bullet or FreeType or Both, the following pops up

Warning

I do not get why?

Solution

The Bullet and FreeType libraries both depend on native code (C or C++) that isn't available in the HTML Libgdx backend.

The HTML Libgdx backend uses Google's GWT project to cross-compile Java bytecodes into Javascript. Thus, only Java code, or APIs that exist in both places can be used. See http://www.badlogicgames.com/wordpress/?p=2308 for more details.