Provides a registry of all Components (instances of Ext.Component or any subclass thereof) on a page so that they can be easily accessed by component id (see get, or the convenience method Ext.getCmp).
This object also provides a registry of available Component classes
indexed by a mnemonic code known as the Component's xtype.
The xtype provides a way to avoid instantiating child Components
when creating a full, nested config object for a complete Ext page.
A child Component may be specified simply as a config object
as long as the correct xtype is specified so that if and when the Component
needs rendering, the correct type can be looked up for lazy instantiation.
For a list of all available xtypes, see Ext.Component.
xtype. (Optional if the config contains a xtype).