cmd shell has incomplete documentation of 'for' loop

FOR switch %variable IN ('command') do %variable

where switch is one of
/D for directories
/F ["options"] for files where options (which I am going to ignore becauase they are not very useful)
/R [[drive:]path] for recursive directory tree walking. takes what's in perens and appends it to directory paths. defaults to current directory. nothing in perens causes no output & lots of cpu time (I think you can eliminate this).

it should also be documented that (at least with for loops), in batch files, %variable should be changed to %%variable. note that in XP this does not seem to work with string manipulation.