You have just grabbed the page's title to place a link on another page, but now you want to add a section title to it to create a section link, but the copy cache is already full. Instead of making two trips back and forth to the page you wish to add the link to, try this...
...use the search box as a quick-and-dirty edit window.
Copy/paste the title into the search box, followed by a "#"
Copy/paste the section title after the "#"
Enclose in double square brackets and copy/paste the whole string to the page you wish to edit.
The search box is also a handy place to store copy text while you copy/paste something else. (But do not forget it is there!)
