The Expression Builder (or Builder Mode) is switched on/off by clicking the Builder Mode icon of the main toolbar . (see screenshot below). The Expression Builder can be switched on in both modes (Evaluation Mode and Debugging Mode). It has has two entry-helper panes: (i) for operators and expressions; and (ii) for functions (see screenshot below). The items in both panes can be shown either grouped hierarchically or as a flat list. Select the option you want in the dropdown list at the top right of each pane (see screenshot below). In the screenshot, both panes show their items in hierarchical groups.
Features of the Expression Builder:
•To view a text description of an item in either entry-helper pane, hover over the item.
•Each function is listed with its signature (that is, with its arguments, the datatypes of the arguments, and the datatype of the function's output).
•If more than one signature exists for a single function name, each signature is listed as a separate function. (These variants are known as overloads of that function name.) In the screenshot above, for example, the contains function is shown twice: once for each of its two signatures.
•Arguments are listed by their names (if any) or by their datatypes. Select the option you want from the dropdown list in the title bar of the Functions pane (circled in green in the screenshot above).
•Double-clicking an item in any of the panes (operator, expression, or function), inserts that item at the cursor location in the expression. Functions are inserted with their arguments indicated by placeholders (# symbols).
•If (i) text is selected in the expression's edit field, and (ii) an operator, expression or function that contains a placeholder is double-clicked to insert it, then the text that was selected is inserted instead of the placeholder. This is a quick way to insert long text (such as a path expression) into an operator, expression, or function.
•You can insert the path to a node in the active document by selecting that node and then clicking the button Copy the XPath of the current selection of the window's main toolbar.
After you have entered a function in the expression, hovering over the function name in the Expression pane displays the function's signature and a text description of the function. If more than one signature exists for a function, these are indicated with an overload factor at the bottom of the display. If you place the cursor within the parentheses of the function and press Ctrl+Shift+Spacebar, you can view the signatures of the various overloads of that function name (see screenshot below).