Help:Section editing demo
Section editing can be turned on by user preference. With the preference chosen, an [edit link] appears to the right of each section demarcated by a heading. For example, with the preference on, there appear two  links on the righthand of this page.
This page is for demonstrating and testing.
This is the second section.
Currently there is no link for editing the part before the first heading, but the URL works, e.g. for this page:
It can be obtained conveniently by using an edit link and changing the number of the section to zero.