clarify custom devices may not spport the required minimum device capabilities

Author: bashbaug

api/glossary.asciidoc

@@ -171,8 +171,9 @@ Converged control flow ::
 Custom Device ::
     A _custom device_ is a specialized _device_ that supports a subset of the
     OpenCL runtime APIs for directed tasks but is not OpenCL conformant.
-    A _custom device_ must implement all of the OpenCL runtime APIs, but may
-    return implementation-defined error codes for unsupported functionality.
+    A _custom device_ must implement all of the OpenCL runtime APIs, but may not
+    support all of the required minimum device capabilities and may return
+    implementation-defined error codes for unsupported functionality.
     See also _Device_.
 
 Data Parallel Programming Model ::

api/opencl_platform_layer.asciidoc

@@ -448,8 +448,9 @@ include::{generated}/api/version-notes/CL_DEVICE_TYPE_ACCELERATOR.asciidoc[]
 include::{generated}/api/version-notes/CL_DEVICE_TYPE_CUSTOM.asciidoc[]
   | Specialized devices that support a subset of the OpenCL runtime APIs for
     directed tasks but are not OpenCL conformant.
-    A custom device must implement all of the OpenCL runtime APIs, but may
-    return implementation-defined error codes for unsupported functionality.
+    A custom device must implement all of the OpenCL runtime APIs, but may not
+    support all of the required minimum device capabilities and may return
+    implementation-defined error codes for unsupported functionality.
 
 | {CL_DEVICE_TYPE_DEFAULT_anchor}