Within Oracle JDeveloper, an XPath expression is considered syntactically valid if it conforms to the XPath 1.0 specification. The XPath Building Assistant warns you about syntactically incorrect XPath functions (for example, a missing parenthesis or apostrophe) by underlining the erroneous area in red. Drag the mouse pointer over this area. The error message displays as a tool tip. The red underlining error disappears after you make corrections. Figure B-12 provides details.

Syntactically valid XPath functions may be semantically invalid. This can cause unexpected errors at runtime. For example, you can misspell the name of an element, variable, function, or part. The XPath Building Assistant warns you about semantic errors by underlining the erroneous area in blue. Drag the mouse pointer over this area. The error message displays as a tool tip. The blue underlining error disappears after you make corrections. Figure B-13 provides details.