Currently the best option to display HEEx is using the HTML language which won't parse and apply syntax highlight to HEEx blocks, nor it will format or enable intellisense.
In order to make it fully work, it needs a language configuration, monarch definition, and intellisense. Not necessarily in the same PR.
A good example implementation is livebook-dev/livebook#1892.
Currently the best option to display HEEx is using the HTML language which won't parse and apply syntax highlight to HEEx blocks, nor it will format or enable intellisense.
In order to make it fully work, it needs a language configuration, monarch definition, and intellisense. Not necessarily in the same PR.
A good example implementation is livebook-dev/livebook#1892.