The spec must be clear about emty array values.

[KonstantinSviridov]

The complete list of properties which accept arrays as values is

• Api.protocols
• Api.mediaType
• Api.documentation
• Api.securedBy
• Resource.securedBy
• Resource.is
• ResourceType.is
• Method.securedBy
• Method.is
• TypeDeclaration.enum
• TypeDeclaration.type
• AnnotationTypeDeclaration.allowedTargets
• OAuth1SecuritySchemeSettings.signatures
• OAuth2SecuritySchemeSettings.scopes

The spec clearly prohibits empty arrays for Api.protocols, Api.documentation and AnnotationTypeDeclaration.allowedTargets.

As for securedBy, the spec states:

The value assigned to the securedBy node MUST be a list of any of the security schemes previously defined in the securitySchemes node of RAML document root.

This sentence can be understood as allowing empty arrays for securedBy. Is it really so?

Finally, the spec says nothing about empty arrays for the remaining properties:

• Api.mediaType
• Resource.is
• ResourceType.is
• Method.is
• TypeDeclaration.enum
• TypeDeclaration.type
• OAuth1SecuritySchemeSettings.signatures
• OAuth2SecuritySchemeSettings.scopes

The TypeDeclaration.type case looks very confusing as it is in fact a case of multiple inheritance where a number of inherited types is zero. So, I would prohibit it.