Stem Environment Notes

The global hash %Stem::Vars::Env is used to store environment values for
the local Hub. These values can be set in a variety of ways:

	Shell environment variables of the form STEM_* are located and
	the STEM_ prefix is removed and the rest of the name is lower
	cased. This name is set to the value of the shell variable.

	The command line of run_stem is parsed for name=value tokens. The
	name/value pair is set in the Stem environment.

	The Stem::TtyMsg module parses its input lines for name=value
	lines (only if the line doesn't contain a leading Cell address).
	White space is allowed around each part and surrounding white
	space is stripped from the value. The name/value pair is set in
	the local Stem environment.

	The Stem::Vars Class Cell (aliased to 'var') can take a
	'set_env' command message. The data field is parse for
	name=value just like Stem::TtyMsg does. This can be used from
	the terminal of any Hub running Stem::TtyMsg to set environment
	variables in any Hub.

The environment values are accessable in several ways:

	A Stem module can import %Stem::Vars::Env via a use Stem::Vars
	statement. The %Env hash can be directly used.

	The Stem::Vars Class Cell supports a 'get_env' command message
	which uses the data field and the environment variable name. It
	returns its value via the normal command/response message
	mechanism.

	The Stem::Vars Class Cell supports a 'status' command message
	which returns a printout of the entire Stem environment for this
	Hub. It returns that via the normal command/response message
	mechanism.

Here are some of the places and ways Stem Environment variables are
used:

	An attribute description can specify an environment variable
	name (via the 'env' option). If this environment variable is
	found it will be used as a default value for this attribute
	overriding the default option value if it was supplied
	too. A passed in value will set the attribute regardless of the
	environment.

	Logical Logs use environment variables to test whether a Log
	Entry is filtered. The value of the variable is compared to the
	Entry severity level with any one of the normal numerical
	boolean tests and it sets the filter flag accordingly.

	The Debug/Trace subsystem uses environment variables in a way
	similar to the Log subsystem. When a Debug routine is created,
	an enviroment name can be set and its value is used as a boolean
	to determine if this call to the Debug sub will happen.

Stem environment values are (and will be) used in many places. If you
use them in configurations or in code, be sure that the names used are
unique.