Puts all Text nodes in the full depth of the sub-tree underneath this Node, including attribute nodes, into a "normal" form where only structure (e.g., elements, comments, processing instructions, CDATA sections, and entity references) separates Text nodes, i.e., there are neither adjacent Text nodes nor empty Text nodes.
DOM Level 2 states :—
https://www.w3.org/TR/DOM-Level-2-Core/#core-ID-normalize
Right now in xmldom, empty text nodes are not removed.