Thank you very much one and all.
Summarizing, if I am cleared to fly runway heading and the wind is calm, regardless of what I've selected on my mode control panel, ATC will see my airplane flying on the runway heading, let's say, 152, and on a straight line.
If there is, say, a crosswind of 15 kts, if I am told to fly runway heading, ATC will see my airplane pointing to 152, but drifting left or right if I've selected heading sel on the MCP; if I have selected track mode, ATC will see me fly fly straight, but my heading will be somewhere around 145 or 165 (depending on the crosswind direction, of course), which wouldn't impress some of you.
I've got the idea.
Thanks again