Mathematica: GOTCHA: If a function is used to generate a control specification (or a grouping of control specifications in a layout) under some circumstances an 'Evaluate@' must be applied to the function for the control specification to be accepted.
The Webel ManGUI` package utilities for Manipulate GUIs Gallery Tutorial [TECHNICAL SLIDE TRAIL] The Webel libraries for Wolfram Mathematica: With SysMLv1 models. Section SECTION: A brief look at the Webel W`Base` utilities for Mathematica