Explanation of `+=`

[soegaard]

Issue description

The documentation of += states the syntax is:

value1 += value2 I suggest changing this to:

identifier += expression or perhaps

variablename += expression

The problem is that identifiers (variablenames) aren't values. Also the righthand side is not restricted to literals - the right hand side can be any expression.

URL(s) of affected page(s)

https://processing.org/reference/addassign.html

Proposed fix