Substituting 4GL variables for constants

You may want your expression to depend on a 4GL data variable rather than on the constant string "HELLO". For this, we use RTL embedded in curly braces (Note that we are now mixing two languages. Within the braces it is RTL, outside it is a PXML expression). The rules for embedding RTL in PXML are:

wherever a numeric constant is allowed in PXML, you can insert an RTL numeric expression (enclosed in curly braces) instead.
wherever a string constant is allowed in PXML, you can insert a RTL string expression (enclosed in curly braces) instead.

The expression "max(10cm,width("HELLO"))" contains one numeric constant "10" and one string constant "HELLO" which can be replaced so that we can write:

max({order_line.titlewidth}cm,width({order_line.title}))

For this expression to be legal, the 4GL variable order_line.titlewidth has to be of type Numeric, and the 4GL variable order_line.title has to be of type String.

Note: You cannot construct a dynamic expression where the function names, such as max or width, or the unit names, such as cm, are dynamic.