XML data manipulation with namespace

Have a look here:
XML Extraction - Handling Namespaces (Tableau, Soap, OASIS types) - Help / Community - UiPath Community Forum

UPD1 - XNamespace Variable Usage

When ns is variable of DataType XNamespace and is holding the Namespace like:
ns = xmlDox.Root.Name.Namespace
then:

Descendants(“{ns}PlanDefinition”)

has to be changed to:
Descendants(ns + "PlanDefinition")