Glad to see JSON&YAML support.
Please consider adding support for YAML anchors.
(Use case: I was hoping to use plantuml to show in-memory data structures layouts, with two objects pointing at one)
http://www.plantuml.com/plantuml/uml/VP0n2iCm34Ltdq9JXq3exYdq9egjfAAsOYmrqDkt3Y4q7Vgtv_ym7mrgMEs5ERb84miRBw8U780Q5VKEFkaty70PdvnYRwJcO8zW9W-tLW1AX5EfeN8nVt3xAgy21SC3PphUiHfF64pFgc6ToQvTvrpXGec5DcEiAE5EknrffRIK1jzZkv-n6TMe_hC6ajXEyGO0
Also it would be nice to fix "Your data does not look like JSON data" when rendering YAML.