Traverses the container’s descendant nodes, calling callback for each declaration node.

If you pass a filter, iteration will only happen over declarations with matching properties.

root.walkDecls(decl => {
  checkPropertySupport(decl.prop)
})

root.walkDecls('border-radius', decl => {
  decl.remove()
})

root.walkDecls(/^background/, decl => {
  decl.value = takeFirstColorFromGradient(decl.value)
})

Like Container#each, this method is safe to use if you are mutating arrays during iteration.