In order to improve legibility in trees, I'd like to introduce two changes:

1. add a structural icon for leaf nodes
2. replace open/close arrows with minus/plus icons

You'll find the rationale for the changes below.

1. Easier to group nodes on same level

User tests show problems with identifying tree levels. In particular, report problems associating nodes with their correct parent nodes.

In the following example, the "class" and "publicKey" properties are on the same level as the "subscribers" folder. For some, however, they are inside the "subscribers" folder.

Part of the problem stems from the fact that leaf nodes do not have structural icons in front of them that vertically line up with their sibling nodes. Another part of the problem is that the tree layout is too generous (see MGNLUI-3161 for a fix for that).

2. Open / close arrows are not easy to discern

Our current open and close icons for folders are hard to read sometimes, since their direction is not clearly identifiable, especially on small representations.

By using minus/plus signs instead of arrows, we can significantly improve the legibility of the open/close state of tree nodes and at the same time make sure they appear lighter. The latter allows the actual icons to stand out more.

Note that trees in older versions of Magnolia had both suggested elements already. They proofed to be clear and effortless to read.