If you define a SimpleBuildWrapper with a @Symbol, you can use it as a block-scoped step inside steps as expected.
If you define a block-scoped Step, you can use it inside steps, or without a block argument in an options block.
But f you define a SimpleBuildWrapper with a @Symbol, you cannot use it in an options block. The syntax is offered in /directive-generator/ (via the wrap metastep apparently), but it does not work at runtime: the symbol is not recognized.
In the file-parameters plugin, this prevents you from using a sleeker syntax for the FileParameterWrapper: