ColdFusion uses the period (.) to separate elements of a complex variable such as a structure, query, XML document object, or external object, as in MyStruct.KeyName. A period also separates a variable scope identifier from the variable name, as in Variables.myVariable or CGI.HTTP_COOKIE.

With the exception of Cookie and Client scope variables, which must always be simple variable types, you cannot normally include periods in simple variable names. However, ColdFusion makes some exceptions that accommodate legacy and third-party code that does not conform to this requirement.

For more information, see About scopes, Using Arrays and Structures, and Using XML and WDDX.