Added support for start-of-input (\A) and end-of-input (\Z) assertions

regex/postfixNode.go

@@ -98,6 +98,13 @@ func newEscapedNode(c rune, inCharClass bool) (postfixNode, error) {
 		if c == 'B' && inCharClass { // Invalid
 			return postfixNode{}, fmt.Errorf("word boundaries are not allowed in character class")
 		}
+	case 'A', 'Z': // A is start of input, Z is end of input (regardless of RE_MULTILINE)
+		if inCharClass {
+			return postfixNode{}, fmt.Errorf("input boundaries are not allowed in character class")
+		} else {
+			toReturn.nodetype = assertionNode
+			toReturn.contents = append(toReturn.contents, c)
+		}
 	case 'n': // Newline character
 		toReturn.nodetype = characterNode
 		toReturn.contents = append(toReturn.contents, '\n')