There is currently no support for YAML in OpenEdge ABL.
It was determined that the Progress Product is functioning as designed.
An enhancement to the product can be requested through the Progress Community via an Ideas submission. Customer feedback is valuable and Idea submissions are monitored by our Product Management team. Enhancement requests are reviewed during the planning phase of each new product release and a list of the enhancements chosen for implementation can be found in the Release Notes documents that accompany each release. Once an Idea is submitted the Progress Software Community will have the opportunity to comment on and vote for the Idea.
For detailed information on how to submit an Idea, please refer to Knowledge Base article 000010839, How to submit an idea for a Progress product enhancement