POSIX-compatible classes

These take the form of "\p{Keyword}" and "\P{Keyword}" for normal and negated variants.

Code	Description	Represents	Notes
Alpha	any letter	`[a-zA-Z]`
Upper	uppercase letters	`[A-Z]`
Lower	lowercase letters	`[a-z]`
Digit	decimal digit	`[0-9]`
Alnum	alphanumeric	`[a-zA-Z0-9]`	this is not the same as `\w` since it excludes "`_`"
XDigit	hexadecimal digit	`[a-fA-F0-9]`
Punct	punctuation	[!"#$%&'()*+,-./:;<=>?@\[\\\]\^_`\|{}~]
Graph	graphic character	`[\p{Alnum}\p{Punct}]`
Print	printable character	`[\x20-\x7E]`	Graph and space (excludes newlines and tab).
Blank	tab or space	`[ \t]`
Space	any whitespace	`\s`
Cntrl	any control character	`[\x00-\x1F\x7F]`

These keywords are case-sensitive - i.e. "\p{alpha}" will cause an error.

Note also that the "[:alpha:]" syntax used by other regex implementations does not work.