You should use the System Tree to insert an attribute for an element only when you are editing in Source view. Dragging an attribute to the page in Page view only adds the text for the attribute—plus an equals sign—to the open page in a displayable format. (In this case it is not added as an attribute of an element.)
To insert an attribute for an element from the
System Tree:
Insert the element.
Drag the attribute from the Language tab of the System Tree to its correct position within the element's brackets.
Enter a value for the attribute.
