title: How to temporary select and edit some lines in a buffer?
body: <p>I'm stuck on this problem. I have a file with almost 10k lines. Some of them should be deleted and I can get an hint from their content, e.g. if they contains a certain pattern "xyz", maybe they must be deleted. So, my idea is to:<br>
  * select only those lines containing each pattern in my list<br>
  * manually inspect them and change the ones actually to be deleted prepending them a "--" (or similar)<br>
  * ...and at the very end, delete all the lines starting with "--".<br>
  As <code>keep-lines</code> actually delete all the un-kept lines (TIL), is there any other way to do what I need? Thanks in advance.</p>