docs: move terms and definitions to separate document

spec/draft/index.rst

@@ -9,6 +9,7 @@ Contents
    :maxdepth: 1
 
    purpose_and_scope
+   terms_and_definitions
    use_cases
    assumptions
 

spec/draft/purpose_and_scope.md

@@ -418,48 +418,6 @@ completed such an implementation may, and are encouraged to, provide details on
 the level of (non-)conformance. For details on how to do this, see
 [Verification - measuring conformance](verification_test_suite.md).
 
-
-* * *
-
-## Terms and Definitions
-
-For the purposes of this specification, the following terms and definitions apply.
-
-<!-- NOTE: please keep terms in alphabetical order -->
-
-**array**:
-a (usually fixed-size) multidimensional container of items of the same type and size.
-
-**axis**:
-an array dimension.
-
-**branch cut**:
-a curve in the complex plane across which a given complex function fails to be continuous.
-
-**broadcast**:
-automatic (implicit) expansion of array dimensions to be of equal sizes without copying array data for the purpose of making arrays with different shapes have compatible shapes for element-wise operations.
-
-**compatible**:
-two arrays whose dimensions are compatible (i.e., where the size of each dimension in one array is either equal to one or to the size of the corresponding dimension in a second array).
-
-**element-wise**:
-an operation performed element-by-element, in which individual array elements are considered in isolation and independently of other elements within the same array.
-
-**matrix**:
-a two-dimensional array.
-
-**rank**:
-number of array dimensions (not to be confused with the number of linearly independent columns of a matrix).
-
-**shape**:
-a tuple of `N` non-negative integers that specify the sizes of each dimension and where `N` corresponds to the number of dimensions.
-
-**singleton dimension**:
-a dimension whose size is one.
-
-**vector**:
-a one-dimensional array.
-
 * * *
 
 ## Normative References

spec/draft/terms_and_definitions.md

@@ -0,0 +1,59 @@
+# Terms and Definitions
+
+For the purposes of this specification, the following terms and definitions apply.
+
+## Normative Keywords
+
+This specification aims to follow [RFC 2119](https://tools.ietf.org/html/rfc2119) and use the following keywords to indicate requirement levels:
+
+**must**:
+a definition or behavior is an absolute requirement of this specification.
+
+**must not**:
+a definition or behavior is an absolute prohibition of this specification.
+
+**should**:
+valid reasons may exist to ignore a definition or behavior in particular circumstances; however, the full implications must be understood and carefully weighed before choosing a different course.
+
+**should not**:
+valid reasons may exist when a particular discouraged behavior is acceptable or even useful; however, the full implications must be understood and carefully weighed before implementing any behavior described by this keyword.
+
+**may**:
+a definition or behavior is truly optional.
+
+## General Terminology
+
+<!-- NOTE: please keep terms in alphabetical order -->
+
+**array**:
+a (usually fixed-size) multidimensional container of items of the same type and size.
+
+**axis**:
+an array dimension.
+
+**branch cut**:
+a curve in the complex plane across which a given complex function fails to be continuous.
+
+**broadcast**:
+automatic (implicit) expansion of array dimensions to be of equal sizes without copying array data for the purpose of making arrays with different shapes have compatible shapes for element-wise operations.
+
+**compatible**:
+two arrays whose dimensions are compatible (i.e., where the size of each dimension in one array is either equal to one or to the size of the corresponding dimension in a second array).
+
+**element-wise**:
+an operation performed element-by-element, in which individual array elements are considered in isolation and independently of other elements within the same array.
+
+**matrix**:
+a two-dimensional array.
+
+**rank**:
+number of array dimensions (not to be confused with the number of linearly independent columns of a matrix).
+
+**shape**:
+a tuple of `N` non-negative integers that specify the sizes of each dimension and where `N` corresponds to the number of dimensions.
+
+**singleton dimension**:
+a dimension whose size is one.
+
+**vector**:
+a one-dimensional array.