diff --git a/current.txt b/current.txt
index 05e8a1f..e519eb0 100644
--- a/current.txt
+++ b/current.txt
@@ -267,7 +267,7 @@
 ad8a28ca3a5549fb9bc24cf5f80ac8f660cc27be885210d76266780aa52ddb8d android.hardware.keymaster@3.0::types
 5804ca86611d72e5481f022b3a0c1b334217f2e4988dad25730c42af2d1f4d1c android.hardware.neuralnetworks@1.0::IDevice
 12e8dca4ab7d8aadd0ef8f1b438021938e2396139e85db2ed65783b08800aa52 android.hardware.neuralnetworks@1.0::IExecutionCallback
-18e6885e184fe48401c2c53f1d1b8bfb07240f40c81ae6b9d2e336fca6efdbb7 android.hardware.neuralnetworks@1.0::types
+86b77e06da756a76aa3685be88765852dd982a86d8c90b8b4fc1130ed4184c8f android.hardware.neuralnetworks@1.0::types
 d4840db8efabdf1e4b344fc981cd36e5fe81a39aff6e199f6d06c1c8da413efd android.hardware.radio@1.0::types
 f96cbc59dfe16c8d0c2a7e06db24d8738a6328b6e90f7b8e1640ea2b4600debd android.hardware.radio@1.1::ISap
 2d86929794795e5c70f4fdb5073485fd05835c9c6f496116687c3d9f32e6df3e android.hardware.radio@1.2::ISap
diff --git a/neuralnetworks/1.0/types.hal b/neuralnetworks/1.0/types.hal
index 4efa13a..1ae1726 100644
--- a/neuralnetworks/1.0/types.hal
+++ b/neuralnetworks/1.0/types.hal
@@ -1519,6 +1519,41 @@
 
     /**
      * Dimensions of the operand.
+     *
+     * For a scalar operand, dimensions.size() must be 0.
+     *
+     * For a tensor operand, dimensions.size() must be at least 1;
+     * however, any of the dimensions may be unspecified.
+     *
+     * A tensor operand with all dimensions specified has "fully
+     * specified" dimensions. Whenever possible (i.e., whenever the
+     * dimensions are known at model construction time), a tensor
+     * operand should have (but is not required to have) fully
+     * specified dimensions, in order to enable the best possible
+     * performance.
+     *
+     * If a tensor operand's dimensions are not fully specified, the
+     * dimensions of the operand are deduced from the operand
+     * dimensions and values of the operation for which that operand
+     * is an output.
+     *
+     * In the following situations, a tensor operand's dimensions must
+     * be fully specified:
+     *
+     *     . The operand has lifetime CONSTANT_COPY or
+     *       CONSTANT_REFERENCE.
+     *
+     *     . The operand has lifetime MODEL_INPUT or MODEL_OUTPUT. Fully
+     *       specified dimensions must either be present in the
+     *       Operand or they must be provided in the corresponding
+     *       RequestArgument.
+     *       EXCEPTION: If the input or output is optional and omitted
+     *       (by setting the hasNoValue field of the corresponding
+     *       RequestArgument to true) then it need not have fully
+     *       specified dimensions.
+     *
+     * A tensor operand with some number of unspecified dimensions is
+     * represented by setting each unspecified dimension to 0.
      */
     vec<uint32_t> dimensions;
 
@@ -1662,10 +1697,19 @@
     /**
      * Updated dimension information.
      *
-     * If dimensions.size() > 0, dimension information was provided along with
-     * the argument. This can be the case for models that accept inputs of
-     * varying size. This can't change the rank, just the value of the
-     * dimensions that were unspecified in the model.
+     * If dimensions.size() > 0, dimension information was provided
+     * along with the argument. This can be the case for models that
+     * accept inputs of varying size. This can't change the rank, just
+     * the value of the dimensions that were unspecified in the
+     * model. If dimensions.size() > 0, then all dimensions must be
+     * specified here; and any dimension that was specified in the
+     * model must have the same value here.
+     *
+     * If the dimensions in the model are not fully specified, then
+     * they must be fully specified here, unless hasNoValue is set to
+     * true. If the dimensions in the model are fully specified, then
+     * either dimensions.size() may be 0, or the dimensions in the
+     * model must be identical to the dimensions here.
      */
     vec<uint32_t> dimensions;
 };