You are probably talking about the [] used on openEHR coded terms, i.e. the usual [snomed::123456789] and similar. In the Task Planning ecosystem, I removed these brackets because they interfere with JSON and other common usages of brackets (usually, to indicate an array or list of things). Instead, I changed the syntax so that coded terms start with a ‘#’ character. See here for an example. If you scroll down, you’ll start seeing things like #low, #normal, #ipi_intermediate_low_risk and so on. Each of the strings ‘low’ etc is the symbolic name of a term local to the Decision Logic Module, i.e. the equivalent of an at-code (but not an id-code) in ADL2. I have not used any external codes directly in this syntax, but they would look like this: #snomed::123456789, which is easy enough to parse.
This is of course yet another piece of custom syntax that JSON, YAML etc know nothing about - but so are other elements of the various flat syntaxes in use in openEHR. Treat it as another idea for the current discussion.