To open an article element in the source pane, just double-click it in the article tree.

Alternatively, right-click it in the article tree, and then click Edit Element as Text. If the article tree is not displayed, see Show/hide article tree.

See also

Automatically open article elements on article opening

And also

End article element editing in the source pane

Abandon changes of the article element in the source pane

Resize article elements in the source pane