Problem
1. Use your favorite search engine to figure out what are the differences between SGML, HTML 5, XML, HTML 4.01, and XHTML.
2. Convert the following hexadecimal numbers to decimal: 2A3, 321, 16, 24, F3.
3. Write a recursive function, hex Value, that converts a hexadecimal string to a decimal integer. If the string passed in has a length of zero, the function will return the integer zero. Otherwise it will return the integer value corresponding to the last character in the string, plus 16 times the hex Value of the rest of the string. The ord function might be useful in determining the integer value of a single-character string.