Maple uses Henry Spencer's RegExp for regular expressions. Due to this you aren't able to use \b for word boundaries. Instead you should use [[:<:]]
for the beginning of word boundaries and [[:>:]]
for end of word boundaries.
Some examples are below:
restart
with(StringTools):
test1:="these are words";
test2:="notwords";
test3:="words at the begining";
RegMatch("[[:<:]]words[[:>:]]",test1); #True
RegMatch("[[:<:]]words[[:>:]]",test2); #False
RegMatch("words[[:>:]]",test2); #True
RegMatch("[[:<:]]words",test2); #False
RegMatch("[[:<:]]words",test1); #True
RegMatch("[[:<:]]words[[:>:]]",test3); #True
RegMatch("^words[[:>:]]",test3); #True
RegMatch("^words[[:>:]]",test1); #False
For more information please see our help pages: