### What needs to get done Not exactly sure as the implementation of advanced grammar seems to be in the Snapcraft project, will that be reusable here? ### Why it needs to get done Hello, I would like to implement the following Snapcraft part definition: ```yaml parts: main: plugin: cmake cmake-parameters: - to armhf: - -DGGML_VULKAN=OFF - else: - -DGGML_VULKAN=ON ``` However this errors with: ```text $ snapcraft pack --debug Bad snapcraft.yaml content: - input should be a valid string (in field 'parts.main.cmake-parameters[10]') - input should be a valid string (in field 'parts.main.cmake-parameters[11]') ``` as (AFAICT) plugin parameters do not have advanced grammar support. This feature is especially helpful in Snapcraft as architecture-specific build configurations are quite common.