(Addition Assignment); And - MACROMEDIA FLASH 8-FLASH LITE 1.X ACTIONSCRIPT LANGUAGE Reference

+= (addition assignment)

Availability
Flash Lite 1.0.
Usage
expression1 += expression2
Operands
expression1, expression2
Description
Operator (arithmetic compound assignment); assigns
expression1 + expression2
same result:
x += y;
x = x + y;
All the rules of the addition (
Example
The following example uses the addition assignment (
by the value of :
y
x = 5;
y = 10;
x += y;
trace(x);// output: 15
See also
+ (numeric add)

and

Availability
Flash Lite 1.0.
Usage
condition1 and condition2
Operands
condition1, condition2
Numbers or strings.
. For example, the following two statements have the
) operator apply to the addition assignment (
+
Conditions or expressions that evaluate to
the value of
expression1
) operator to increase the value of
+=
true
) operator.
+=
x
or .
false
and 81