Describe how to convert non-string primitives for protocols which only support strings (open-telemetry#2343)

* Describe how to handle converting non-string primitives for protocols that only support strings

* update wording to make clear that only non-string values are converted to strings

* unify language

* Update specification/common/common.md

Co-authored-by: Joshua MacDonald <jmacd@users.noreply.github.com>

Co-authored-by: Joshua MacDonald <jmacd@users.noreply.github.com>
Co-authored-by: Bogdan Drutu <bogdandrutu@gmail.com>

Author: 3 people

specification/common/common.md

@@ -26,8 +26,9 @@ An `Attribute` is a key-value pair, which MUST have the following properties:
 - The attribute value is either:
   - A primitive type: string, boolean, double precision floating point (IEEE 754-1985) or signed 64 bit integer.
   - An array of primitive type values. The array MUST be homogeneous,
-    i.e., it MUST NOT contain values of different types. For protocols that do
-    not natively support array values such values SHOULD be represented as JSON strings.
+    i.e., it MUST NOT contain values of different types.
+
+For protocols that do not natively support non-string values, non-string values SHOULD be represented as JSON-encoded strings.  For example, the expression `int64(100)` will be encoded as `100`, `float64(1.5)` will be encoded as `1.5`, and an empty array of any type will be encoded as `[]`.
 
 Attribute values expressing a numerical value of zero, an empty string, or an
 empty array are considered meaningful and MUST be stored and passed on to