Document areas where GinkgoT() behaves differently from testing.T

adresses #1331

docs/index.md

@@ -5480,6 +5480,11 @@ When using Gomock you may want to run `ginkgo` with the `-trace` flag to print o
 
 Similarly for third party libraries which accept a `testing.TB` interface, use the `GinkgoTB()` function. This function returns a struct wrapper around `GinkgoT()` which satisfies the `testing.TB`interface. If you need to use any Ginkgo-specific methods you can access the wrapped `GinkgoT()` instance using `GinkgoTBWrapper.GinkgoT`.
 
+In general, `GinkgoT()` attempts to mimic the behavior of `testing.T` with the exception of the following:
+
+- `Error`/`Errorf`: failures in Ginkgo always immediately stop execution and there is no mechanism to log a failure without aborting the test.  As such `Error`/`Errorf` are equivalent to `Fatal`/`Fatalf`.
+- `Parallel()` is a no-op as Ginkgo's multi-process parallelism model is substantially different from go test's in-process model.
+
 ### IDE Support
 Ginkgo works best from the command-line, and [`ginkgo watch`](#watching-for-changes) makes it easy to rerun tests on the command line whenever changes are detected.
 

ginkgo_t_dsl.go

@@ -15,6 +15,11 @@ GinkgoT() is analogous to *testing.T and implements the majority of *testing.T's
 GinkgoT() takes an optional offset argument that can be used to get the
 correct line number associated with the failure - though you do not need to use this if you call GinkgoHelper() or GinkgoT().Helper() appropriately
 
+GinkgoT() attempts to mimic the behavior of `testing.T` with the exception of the following:
+
+- Error/Errorf: failures in Ginkgo always immediately stop execution and there is no mechanism to log a failure without aborting the test.  As such Error/Errorf are equivalent to Fatal/Fatalf.
+- Parallel() is a no-op as Ginkgo's multi-process parallelism model is substantially different from go test's in-process model.
+
 You can learn more here: https://onsi.github.io/ginkgo/#using-third-party-libraries
 */
 func GinkgoT(optionalOffset ...int) FullGinkgoTInterface {