Q:

QGIS Marker Expressions

I am working on writing basic expressions to control the Marker Properties. My previous question on the syntax for color was graciously answered , but I soon realized that I need to know the syntax for all the properties like , size, outline, angle. Is there a place I can find them all

A:

According to your previous question (Building Expressions for QGIS Markers) you have to click on Data defined override button and choose Description..., there are information about possible values and and wich value type is acceptable. String values in syntax have to be in simple quotes like 'my_value'.
1.

2.

For your previous example - expression changing Fill style:
CASE WHEN "STATUS" = 'ON AIR' THEN 'b_diagonal' 
WHEN "STATUS" = 'OFF AIR' THEN 'f_diagonal'
END

