If a line matches this pattern, then all the lines after it should be unindented once (until another rule matches).
If a line matches this pattern, then all the lines after it should be indented once (until another rule matches).
If a line matches this pattern, then only the next line after it should be indented once.
If a line matches this pattern, then its indentation should not be changed and it should not be evaluated against the other rules.
Describes indentation rules for a language.