More references to TRACE logging level:

* "CUSTOM_TRACE = 5 # Mapping for zLOG.TRACE" in Zope zLOG
  https://github.com/zopefoundation/zLOG/blob/master/src/zLOG/EventLogger.py#L29

* Runlevel = stem.util.enum.UppercaseEnum('TRACE', 'DEBUG', 'INFO', 'NOTICE', 'WARN', 'ERROR')
  TRACE, DEBUG, INFO, NOTICE, WARN, ERR = list(Runlevel)
  https://stem.torproject.org/_modules/stem/util/log.html

* "TRACE = 5 # Trace log level."
  "An extension of Python's option parser."
  https://github.com/mikeorr/WebHelpers2/blob/master/unfinished/logging_optparse.py#L14

* "TRACE = 5"
  http://www.taurus-scada.org/en/latest/_modules/taurus/core/util/log.html

* "TRACE = 9"
  "bokeh: Interactive plots and applications in the browser from Python"
  https://pypkg.com/pypi/bokeh/f/bokeh/util/logconfig.py

* "With custom log levels: (...) TRACE = 5" (an example in the doc)
  https://pypi.python.org/pypi/colorlog

Note: Zope zLOG also has a "CUSTOM_BLATHER = 15 # Mapping for zLOG.BLATHER" level.