Extended regular expressions were introduced in Section 8.4, "Extended Regular Expressions" in Chapter 8. The additional metacharacters available in elvis are:
\+\?\@\=Indicates where to put the cursor when the text is matched.
For instance, hel\=lo would put
the cursor on the second l in the
next occurrence of hello.
\{...\}Describes an interval expression, such as
x\{1,3\} to match
x, xx,
or xxx.
POSIX bracket expressions (character classes, etc.) are not
available,[2]
nor is alternation with the | character or
grouping with parentheses.
[2] Well, in elvis 2.0 they're there, they just don't work. This is fixed in elvis 2.1.