whether a long key can be specified with an unambiguous substring
whether prefixing a boolean key with "no-" will cause that option to be set to false (long key mode only)
whether multiple short keys can be clustered into a single argument
Some(true) means that all values must be collapsed with their key in a single argument (with '=' delimiting for long key mode and nothing delimiting in short key mode).
Some(true) means that all values must be collapsed with their key in a single argument (with '=' delimiting for long key mode and nothing delimiting in short key mode). Some(false) means that collapsing is prohibited. None means either style is allowed.
the prefix that indicates an option key is coming
suppress UsageExceptions (can be useful during pattern matching)
stop parsing options when the first bare word is encountered, otherwise, continue looking for options after the bare word
use long keys (field name, decamelized) instead of short keys (first character of field name)
regexp to split multiple values in a single argument