Tags length limit seems to be 30 characters
I was having a problem seeing some tags in TortoiseHg. I went to command line and typed "hg tags" and it also didn't show the same tags. After manually editing .hgtags file and commits, I saw that tags would work if there was 30 characters or less and at 31 characters length, they would not show up.
For example: Issue683_SystemTest_Preliminary (does not work) Issue683_SystemTest_Preliminar (works)
I expect there would be no limit on tag length. Nowhere in the documentation is that stated.
TortoiseHg for MSWindows, v2.2 Mercurial Distributed SCM (version 2.0)