What is an Expression in PaintCode and where can I find Expression syntax/functions reference?

PaintCode allows you to create variables. Variables are values with a name. For example, you can create a variable with name “dimension” and value “123”. You can then connect this variable to many shapes in your drawing, specifying that you wish all of those shapes to be the same height as is the value of the “dimension” variable. When you change the variable to some other value, let’s say, 246, the height of all your shapes will automatically change from 123 to 246, too.

Expressions are mathematical formulas that you can use to make variables depend on other variables. For example, you can make a new variable called “doubleDimension” and define its value using an expression as “dimension + dimension”. Alternatively, you can use the expression “2 * dimension” to achieve the same effect. Expressions and variables are very powerful. You can use them to create dynamic drawings that are impossible to create in other tools.

Please, check out the "Documentation for Expression syntax/functions" and example project.