As a follow up Devons comment, the examples in the POS function are prefixed by a statement:
Given A$="The quick brown fox":
Based on this being the case and A$ has the specified value, the examples of the function formats and what they will return are all correct.
Your trainee likely missed the fact that A$ had to have a value which is why they misunderstood the examples.
As for the the examples not being complete/functional statements, the assumption is that the reader has a basic understanding of what a function is and how should be used.
Lastly, your earlier comment about GOTO is inappropriate given that most PxPlus applications have come from older programs where GOTO was generally used extensively. Given that often documentation is used by trainee programmers (as you mentioned), these individuals need to understand the use of the GOTO directive if they hope to maintain older applications. Not providing examples using GOTO would leave these trainees at a disadvantage, much as not including text mode directives such as INPUT or ACCEPT given newer application are primarily graphical. The that point, even not showing the use of line numbers, would also be problem for new hires attempting to learn the environment.
Not every PxPlus application is fully graphical using structured programming techniques without line numbers or GOTOs.