Reading the comments makes me want to qualify my answer: I've only ever seen headers at the top of a story, where everyone is pretty much forced to read them. With that in mind, I gave the "I hate character death warnings!" type of answers. I strongly dislike the expectations that you must spoil your story in any way past a summary/teaser; yes, some people have things that squick them, but Tolkien didn't have to print "WARNING: Character death!" in Fellowship, nor did Silence of the Lambs trailers explicitly tell viewers that they should look out for... well, X, Y, and Z. In my view, if you know that death/suicide/cutting/abuse/etc. is a trigger for you that you simply cannot read, you can get safe recs from your friends rather than expect to have major plot points spoiled for everyone right off the bat.
However.
The idea of warnings on a different page, or below the fic completely changes my POV on this. If people could opt-in to reading what is basically the author spoiling her own story, it's... well, it's like people putting show spoilers behind a cut rather than a front page entry. It shows respect for all involved people, and everybody's happy! While I think it's a bit much to say that X character dies (doing so would have ruined Paterfamilias, for example), "Character Death" in a safely tucked-away warning is a nice compromise for all involved parties.
(Now that my idealogical rant about everyone being presented with spoilers in the form of headers is over: if I'm told a fic has character death, I'm more likely to read it. Yay, dark! If a fic tells me in headers right off the bat, I'm less likely to read it because of my strong distaste for that fandom convention. So... I am a strange and contradictory person. Basically: opt-in headers are good. Yes.)
no subject
However.
The idea of warnings on a different page, or below the fic completely changes my POV on this. If people could opt-in to reading what is basically the author spoiling her own story, it's... well, it's like people putting show spoilers behind a cut rather than a front page entry. It shows respect for all involved people, and everybody's happy! While I think it's a bit much to say that X character dies (doing so would have ruined Paterfamilias, for example), "Character Death" in a safely tucked-away warning is a nice compromise for all involved parties.
(Now that my idealogical rant about everyone being presented with spoilers in the form of headers is over: if I'm told a fic has character death, I'm more likely to read it. Yay, dark! If a fic tells me in headers right off the bat, I'm less likely to read it because of my strong distaste for that fandom convention. So... I am a strange and contradictory person. Basically: opt-in headers are good. Yes.)