Dynamic References to Global Variables
Visualforce pages can use dynamic bindings to reference global variables in their markup. Global variables allow you to access information about the current user, your organization, and schema details about your data. The list of global variables is available in the Global Variables, Functions, and Expression Operators appendix.
Referencing a global variable is the same as referencing sObjects and Apex classes—you
use the same basic pattern, where reference is a global
variable:
reference[expression]