WalkDownExpr works just like WalkUpExpr but it walks the tree down, visiting all children.

WalkUpExpr allows to iterate a promQLNode node looking for parents of specific type.

WalkUpParent works like WalkUpExpr but checks the parent (if present) instead of the node itself.

Use insread of StrictError.

PromQLNode is used to turn the parsed PromQL query expression into a tree.