Please DO NOT TRY TO USE it for now. Thanks for your comprehension!
x is an XStringPartialMatches object. subpatterns(x):
Not ready yet.
pattern(x):
Not ready yet.
x is an XStringPartialMatches objects,
and i can be a numeric or logical vector. x[i]:
Return a new XStringPartialMatches object made of the selected views.
i can be a numeric vector, a logical vector, NULL or missing.
The returned object has the same subject as x.
letter