Why don't you get it from the Source: fltk.org/documentation?
Instead of using trial & error Method ???
Since this is a freeBasic programming forum, I was hoping to keep as close to FBC language as possible. I could be wrong about all this, maybe freeBasic is changing to C++.
Introduction to FLTK
This manual describes FLTK version 2.0, a cross-platform C++ Graphical User Interface (GUI) toolkit. Each of the "related pages" in this manual is designed as a tutorial for using FLTK, while the main sections provide a complete reference for all FLTK widgets and functions.
FLTK (pronounced "fulltick") is a LGPL'd C++ graphical user interface toolkit for X (UNIX®), OpenGL®, Microsoft® Windows®, OS/X, and several other platforms. It was originally developed by Mr. Bill Spitzak and is currently maintained by a small group of developers across the world with a central repository in the US.
Again, it is greatly appreciated that D.J.Peters took the time and energy to make FLTK available for freeBasic. Not sure what enhancements, if any, were made by D.J.Peters to be able to make FLTK run in FBC, but he would be the one to know what is consistent. Now if we can get back on topic.