缩写词EE在.NET参考源中是什么意思

在String类的.NET引用源中，有各种引用EE的注释。

第一个是在m_stringLength:上

//NOTE NOTE NOTE NOTE
//These fields map directly onto the fields in an EE StringObject.  See object.h for the layout.
//
[NonSerialized]private int  m_stringLength;

再次为.Empty:找到

// The Empty constant holds the empty string value. It is initialized by the EE during startup.
// It is treated as intrinsic by the JIT as so the static constructor would never run.
// Leaving it uninitialized would confuse debuggers.
//
//We need to call the String constructor so that the compiler doesn't mark this as a literal.
//Marking this as a literal would mean that it doesn't show up as a field which we can access 
//from native.
public static readonly String Empty;

它也在Length:上

// Gets the length of this string
//
/// This is a EE implemented function so that the JIT can recognise is specially
/// and eliminate checks on character fetchs in a loop like:
///        for(int I = 0; I < str.Length; i++) str[i]
/// The actually code generated for this will be one instruction and will be inlined.

我敢说，它可能与E引擎有关，或者是E外部引擎，但我希望有一个实际的参考来定义它是什么。

EE是什么意思？