Where is CodeGenerationTools

In entity framework T4 templates, I can use class CodeGenerationTools.

For example:

void WriteProperty(**CodeGenerationTools** code, EdmProperty edmProperty)
{
    WriteProperty(Accessibility.ForProperty(edmProperty),
                  code.Escape(edmProperty.TypeUsage),
                  code.Escape(edmProperty),
                  code.SpaceAfter(Accessibility.ForGetter(edmProperty)),
                  code.SpaceAfter(Accessibility.ForSetter(edmProperty)));
}

However, I can't find where this class is defined.

Which assembly does it come from? What are its members?

Thanks