A few other ideas for possible variables...
{raw} = 1 if file is a RAW file, otherwise 0
This could be very useful when conditional expressions is eventually implemented
{filetype} = filename extension (e.g. JPG, NEF, CR2, etc.), or {extension}, {ext}, etc.
{saturation} = Camera Saturation Setting (IEXF tag 0xA409)
Nikon specific data:
{colorspace} = Color Space "sRGB" or "Adobe RGB" (MakerNotes tag 0x001E)
{wbft} = White Balance Fine Tuning Value (MakerNotes tag 0x000B)
{hueadjust} = Hue Adjustment Value (MakerNotes tag 0x0092)
{shootingmode} = Shooting Mode (MakerNotes tag 0x0089)
{hsc} = High Speed Crop Mode on/off (MakerNotes tag 0x001B)
{nr} = Noise Reduction on/off (MakerNotes tag 0x0095)
Special Characters
{c} = Copyright Symbol "©" (ISO-8859-1 char 0169, Unicode char 0x00A9)
{ff} = Function Symbol "ƒ" (Unicode char 0x0192) - useful when showing f-stop
{d} = Degree Symbol "°" (ISO-8859-1 char 0176, Unicode char 0x00B0)
{tm} = Trademark Symbol "™"(Unicode char 0x2122)
{rtm} = Registered Trademark Symbol "®"(ISO-8859-1 char 174, Unicode char 0x00AE)
Thanks,
Ian