You must be in Command mode for the Expression option to be enabled.
To enter an expression by using the Expression Builder dialog box (Edit | Expression):
Open the Edit window (View | Edit Window).
Place the Edit window into Command mode (View | Command Mode).
Move the cursor to an editable field where you want to insert the expression.
Press the F2 key while the cursor is on a field that allows expressions. The Expression Builder dialog box appears. The Expression Builder dialog box lists all of the operators, operands, and functions. The following can be referenced through this dialog box:
Available expression types
Variables
Features
Dimensions
Alignments
Comments
Select the expression element type from the first drop-down list. Depending on your selection, other combination boxes appear.
Select the desired ID from the ID drop-down list.
Select an extension from the Extension drop-down list.
Select another extension from the Second Extension drop-down list. If the expression is usable, the Add button becomes available.
Click the Add button. The expression appears in an edit box.
Click the OK button. The expression now appears where your cursor is in the Edit window.
You can also open the Expression Builder dialog box from these other dialog boxes:
The If Expression dialog box - Select Insert | Flow Control Command | If Goto. Click on the Expression button.
The Assignment dialog box - Select Insert | Assignment. Click the Assign To or Assign From button.
Once the expression is created, PC-DMIS automatically inserts the expression at the next legal position in the Edit window.