`mv()` marks a named observation- or entity-aligned `axis_block` for
expansion by [compile_design()]. It is meaningful only inside a formula.
Usage
mv(block, components = NULL)
Arguments
- block
Unquoted block name, optionally qualified by an entity name,
such as `motion` or `stimulus.visual_pca`.
- components
Optional component positions or stable component IDs.
Value
This function always errors when evaluated directly.