The ^ is used as a wildcard search character within the string parameter for replacing known and sometimes unknown strings within strings. It matches any character. Note that ^ is a normal character, not a control character. See the r/^^^// example below.
Using attribute marks with the r command:
The control shift ^ represents an attribute mark in the Editor. Used with the r command, it has the effect of terminating the line. See the examples below.
Replaces the first 3 characters (wildcards, or ^) of the current line with null, (that is, deletes the first three characters).
r/^^^//
Replaces the first occurrence of the string, abc, with an attribute mark (control shift ^), terminating the line prior to the string, abc.
r/abc/^
Replaces all characters on the current attribute with null, leaving the current attribute intact, but empty.
ru/^//