What is "T:" when used in CREW
This is essentially an annotation that the code link refers to when the compiler generates identifiers in the documentation. Here T indicates that the name of the referenced System.Windows.Form.Control is a type, not a namespace or other member.
The text of System.Windows.Form.Control can have different meanings. It can be a namespace, for example, or a Control element of the System.Windows.Form object. This helps to describe what exactly.
You can see additional information about other conventions that the compiler uses in docs .
Other prefixes are as follows:
N namespace T type: class, interface, struct, enum, delegate F field P property (including indexers or other indexed properties) M method (including such special methods as constructors, operators, and so forth) E event ! error string