Any capitalisation wizards around?

[lady_karelia]

If in a sentence, a reference is made to the "subject line" of an e-mail, what would be the correct spelling? "Subject line", "subject line", or "Subject Line".

Example: There was no ticket number found in the Subject line, or the ticket number could not be parsed correctly.

Is "subject" and "line" capsed, not capsed, or is only "subject" capsed?

If you could help me solve this riddle, I'll be forever grateful because it is nagging me now.

Comments

[juli-min.livejournal.com]

To be honest, the few times I used that, I capsed only "subject". Nobody has yet complained about that, so I guess it's at least not wrong.