Fix combined sampler documentation and warning (#6207)

* Fix combined sampler documentation and warning

* Update comment, show detailed '-fvk-t-shift' message in warning instead of generic '-fvk-xxx-shift'

* format code

---------

Co-authored-by: slangbot <186143334+slangbot@users.noreply.github.com>

1 files changed, 8 insertions, 1 deletions

diff --git a/docs/user-guide/a2-01-spirv-target-specific.md b/docs/user-guide/a2-01-spirv-target-specific.md
index dcbe44e96..5090caacf 100644
--- a/docs/user-guide/a2-01-spirv-target-specific.md
+++ b/docs/user-guide/a2-01-spirv-target-specific.md
@@ -20,7 +20,14 @@ Combined texture sampler
 Slang supports Combined texture sampler such as `Sampler2D`.
 Slang emits SPIR-V code with `OpTypeSampledImage` instruction.
 
-You can specify two different register numbers for each: one for the texture register and another for the sampler register.
+For SPIR-V targets, explicit bindings may be provided through a single `vk::binding` decoration.
+```
+[[vk::binding(1,2)]]
+Sampler2D explicitBindingSampler;
+```
+
+For other targets (HLSL or others) where combined texture samplers are _not_ supported intrinsicly, they are emulated by Slang using separate objects for Texture and Sampler.
+For explicit binding on such targets, you can specify two different register numbers for each: one for the texture register and another for the sampler register.
 ```
 Sampler2D explicitBindingSampler : register(t4): register(s3);
 ```