XPath defines literal forms for strings and numbers. Numbers have more or less the same form as double literals in Java. That is, they look like 72.5, -72.5, .5321, and so forth. XPath only uses floating point arithmetic, so integers like 42, -23, and 0 are also number literals. However, XPath does not recognize scientific notation such as 5.5E-10 or 6.022E23.
XPath string literals are enclosed in single or double quotes. For example, "red" and 'red' are different representations for the same string literal containing the word red.
There are no boolean or node-set literals. However, the true() and false() functions sometimes substitute for the lack of boolean literals.