No reasonably sized keyboard could possibly include all the characters in Unicode. U.S. keyboards are especially weak when it comes to typing in foreign languages with unusual accents and non-Latin scripts. XML allows you to use either character references or entity references to address this problem. In general, named entity references like Ě should be preferred to character references like ě because they're easier on the human beings who have to read the source code.

Everything you need to know about XML 1.1 can be summed up in two rules.

Despite the rapid growth of Unicode in the last few years, the sad fact is that many text editors and other tools are still tied to platform- and nationality-dependent character sets such as Windows-1252, MacRoman, and SJIS. The only characters all these sets have in common are the 128 ASCII letters, digits, punctuation marks, and control characters. These characters are the only ones that can be reliably displayed and edited across the wide range of computers and software in use today. Thus, if it's not too big a problem, try to limit your markup to the ASCII character set. If you're writing in English, this is normally not a problem.

Although XML declarations are optional, every XML document should have one. An XML declaration helps both human users and automated software identify the document as XML. It identifies the version of XML in use, specifies the character encoding, and can even help optimize the parsing. Most importantly, it's a crucial clue that what you're reading is in fact an XML document in environments where file type information is unavailable or unreliable.