// d Any digit character
// w An alphanumeric character (“word character”)
// s Any whitespace character (space, tab, newline, and similar)
// D A character that is not a digit
// W A nonalphanumeric character
// S A nonwhitespace character
// . Any character except for newline
// /abc/ A sequence of characters
// /[abc]/ Any character from a set of characters
// /[^abc]/ Any character not in a set of characters
// /[0-9]/ Any character in a range of characters
// /x+/ One or more occurrences of the pattern x
// /x+?/ One or more occurrences, nongreedy
// /x*/ Zero or more occurrences
// /x?/ Zero or one occurrence
// /x{2,4}/ Two to four occurrences
// /(abc)/ A group
// /a|b|c/ Any one of several patterns
// /d/ Any digit character
// /w/ An alphanumeric character (“word character”)
// /s/ Any whitespace character
// /./ Any character except newlines
// // A word boundary
// /^/ Start of input
// /$/ End of input