You should see
Regular expression: man Matches A man, a plan, a canal. Panama
Regular expression: .*man Matches: A man, a plan, a canal. Panama
Regular expression: th.n Matches: than
Regular expression: th.n Matches: then
Regular expression: th.n Matches: thing
Regular expression: be+ Matches: behind
Regular expression: be+ Matches: bee
Regular expression: th? Matches: theme
Regular expression: th? Matches: tan
Regular expression: \d Does NOT match than
Regular expression: \d Matches: 123
Regular expression: \D Matches: than
Regular expression: \D Does NOT match 123
Regular expression: \w Matches: than
Regular expression: \w Matches: 123
Regular expression: \W Does NOT match than
Regular expression: \W Does NOT match 123