I have tested the above on Oracle DB version 8.1.7 and it worked.

Here is some more information from the OWA_PATTERN package specification:

Assertions:
^ Matches the beginning of a line (or string)
$ Matches the end of a line (or string)

Quantifiers:
{n,m} Must match at least n times, but not more than m times
{n,} Must match at least n times
{n} Must match exactly n times.
* 0 or more occurances
+ 1 or more occurances
? 0 or 1 occurance(s)

Legal atoms:
. matches any character except \n

A list of characters in square brackets [] is a class of characters,
for example [0-9] indicates match any character from 0 to 9.

\n matches newlines
\t matches tabs
\d matches digits [0-9]
\D matches non-digits [^0-9]
\w matches word characters (alphanumeric) [0-9a-z_A-Z]
\W matches non-word characters [^0-9a-z_A-Z]
\s matches whitespace characters [ \t\n]
\S matches non-whitespace characters [^ \t\n]
\b matches on “word” boundaries (between \w and \W)

A backslashed x followed by two hexadecimal digits, such as \x7f,
matches the character having that hexadecimal value.

A backslashed 2 or 3 digit octal number such as \033 matches the
character with the specified value.

Any other “backslashed” character matches itself.