+/// return true if a unicode char is a space.
+bool isSpace(char_type c);
+
+/// return true if a unicode char is a numeral.
+bool isNumber(char_type c);
+
+/// return whether \p c is a digit in the ASCII range
+bool isDigitASCII(char_type c);
+
+/// return whether \p c is alpha or a digit in the ASCII range
+bool isAlnumASCII(char_type c);
+
+/// return whether \p c is in the ASCII range
+bool isASCII(char_type c);