[Form] Better explaining what `getParent` actually does

[ThomasLandauer]

Main reason for changing this is to stop presenting getParent() of being the "default" (or normal) way of doing it.

• I removed the "PHP extension" note-box, cause the (new) text for getParent() makes it clear what this does.
• I moved finishView() one paragraph up (didn't change anything)
• Moved all getParent-related stuff into its paragraph, and moved it to the top (since it's the most important question in the beginning)