@Jan-Buriánek
Yes, different apps and devices handle it differently. For example:
Program MapSource puts the description in <desc> and <cmt>,
BaseCamp: <desc> and <cmt>,
Oziexplorer: <desc> and <cmt>; (text is truncated to 100 characters),
Garmin Oregon, eTrex Devive: tag <desc>,
app Locus Map: tag <desc>.
There are applications on websites that only support <cmt>, but very rarely. As you write, the best solution seems to be to put the description in the <desc> tag and display it and have it editable in place Edit properties (Add note), 5000 char. And of course export with <desc> included.