Update int64.md (OAI#3232)

Author: ralfhandl

registries/_format/int64.md

@@ -2,7 +2,7 @@
 owner: DarrelMiller
 issue: 
 description: signed 64-bit integer
-base_type: number
+base_type: number, string
 layout: default
 source: https://spec.openapis.org/oas/latest.html#data-types
 source_label: OAS
@@ -16,6 +16,8 @@ Base type: `{{ page.base_type }}`.
 
 The `{{page.slug}}` format represents a signed 64-bit integer, with the range -9223372036854775808 through 9223372036854775807. This format entry is to ensure future versions of OpenAPI maintain compatibility with [OpenAPI 3.0.x](https://spec.openapis.org/oas/v3.0.0).
 
+Representation as a JSON string is recommended for values outside the 53-bit range (-9007199254740991 through 9007199254740991) as this avoids problems with recipients that parse JSON numbers into [binary64](https://en.wikipedia.org/wiki/Double-precision_floating-point_format) memory representation.
+
 {% if page.issue %}
 ### GitHub Issue
 
@@ -26,4 +28,4 @@ The `{{page.slug}}` format represents a signed 64-bit integer, with the range -9
 ### Remarks
 
 {{ page.remarks }}
-{% endif %}
+{% endif %}