lib/ContextStackTrait.php
public function pushContext()
    {
        $this->contextStack[] = [
            $this->elementMap,
            $this->contextUri,
            $this->namespaceMap,
            $this->classMap,
        ];
    }
public function pushContext()
    {
        $this->contextStack[] = [
            $this->elementMap,
            $this->contextUri,
            $this->namespaceMap,
            $this->classMap,
        ];
    }
Create a new "context".

This allows you to safely modify the elementMap, contextUri or
namespaceMap. After you're done, you can restore the old data again
with popContext.