Mark selectionBehavior as CONDITONAL rather than OPTIONAL

Author: jmandel

docs/specification/1.0.md

@@ -452,7 +452,7 @@ Field | Optionality | Type | Description
 `indicator` | REQUIRED | *string* | Urgency/importance of what this card conveys. Allowed values, in order of increasing urgency, are: `info`, `warning`, `critical`. The CDS Client MAY use this field to help make UI display decisions such as sort order or coloring.
 `source` | REQUIRED | *object* | Grouping structure for the **Source** of the information displayed on this card. The source should be the primary source of guidance for the decision support the card represents.
 <nobr>`suggestions`</nobr> | OPTIONAL | *array* of **Suggestions** | Allows a service to suggest a set of changes in the context of the current activity (e.g.  changing the dose of the medication currently being prescribed, for the `medication-prescribe` activity). If suggestions are present, `selectionBehavior` MUST also be provided.
-`selectionBehavior` | OPTIONAL | *string* | Describes the intended selection behavior of the suggestions in the card. Currently, the only allowed value is `at-most-one`, indicating that the user may choose none or at most one of the suggestions. Future versions of the specification may expand this behavior, so CDS Clients that do not understand the value MUST treat the card as an error. CDS Clients MUST support the value of `at-most-one`.
+`selectionBehavior` | CONDITIONAL | *string* | Required if `suggestions` is non-empty. Describes the intended selection behavior of the suggestions in the card. Currently, the only allowed value is `at-most-one`, indicating that the user may choose none or at most one of the suggestions. Future versions of the specification may expand this behavior, so CDS Clients that do not understand the value MUST treat the card as an error. CDS Clients MUST support the value of `at-most-one`.
 `links` | OPTIONAL | *array* of **Links** | Allows a service to suggest a link to an app that the user might want to run for additional information or to help guide a decision.
 
 #### Source