Function costly 

pub fn costly(rule: FieldRule, tint: Tint, why: &str) -> FieldRule

Mark a rule as one where every answer costs the same thing.

For the axes with no safe direction: whichever value you land on, the workspace gets rewritten. The tint is what draws the row; the Consequence is what Apply reads before carrying the change out.

Both, not either — they answer different questions. The tint says how loudly to draw a field the reader is looking at; the consequence says what happens if they go through with it. A row can be drawn calmly and still be expensive to change.