XML has a special set of characters that cannot be used in normal XML strings. These characters are:

1. & – &
2. < - <
3. > – >
4. ” – "
5. ‘ – '

For example, the following XML string is invalid:

 IBM & Microsoft

Whereas the following is valid XML:

 IBM & Microsoft

?Note that we have replaced ‘&’ with ‘&’ in the second XML string which makes it valid.