Mathematica: Webel: You CAN/MAY use $ in variable names and function names - just not as the first character before a Capital - and it's extremely useful. You won't get sent to Azkaban prison if do you use a $ character!
A constraint property may be shown on a parametric diagram using a rectangle with rounded corners. This graphical shape distinguishes a constraint property from all other properties and avoids the need to show an explicit «constraint» keyword. Otherwise.. Source OMG Systems Modeling Language (SysML) 1.6
