Open the list of blocks that can be added to a region of the layout: the "Add block" dialog of the region.
Examples
When I open the block list of the "Sidebar" region
When I open the block list of the "Footer" region
When we open the block list of the "Header" region
And I open the block list of the "Content" region
When open the block list of the "Top" region
Pattern
When(/^(I |we )*open the block list of the "([^"]*)" region$/, …)
Part of @webship-js/backdrop-cms-steps (github.com/webship/backdrop-cms-steps), a step pack for Webship-js 2.0.x.