QUANTIFIERS
Zero or more, optional
* allows any count including zero. ? makes the previous element optional.
a+ one or more a. Matches "a", "aaa", but not "".a* zero or more a. Matches "aaa" and also the empty string (zero a).a? zero or one a - the a is optional. colou?r matches both color and colour.colou?r matches color and colour: the u may appear once or not at all. `*` is `+` minus the obligation: x* happily matches the empty string, which makes it dangerous alone but powerful after something concrete.
Match both color and colour.
/ /
color scheme
must match: "color"
colour scheme
must match: "colour"
colouur is wrong
must match nothing