Character classes

alnum

Any alpha-numeric character.

alpha

Any alphabetic character.

blank

Any whitespace character that is not a line separator.

cntrl

Any control character.

d

Any decimal digit

digit

Any decimal digit.

graph

Any graphical character.

l

Any lower case character.

lower

Any lower case character.

print

Any printable character.

punct

Any punctuation character.

s

Any whitespace character.

space

Any whitespace character.

unicode

Any extended character whose code point is above 255 in value.

u

Any upper case character.

upper

Any upper case character.

w

Any word character (alphanumeric characters plus the underscore).

word

Any word character (alphanumeric characters plus the underscore).

xdigit

Any hexadecimal digit character.

[[:upper:]] will match any upper case character.
^[[:lower:]].* will match any string that starts with a lower case character.

 syntax is used in all products.