Hovering the mouse cursor over an element set by Select Filter will display that element.
highlighting
When the cursor is over a vertex, the vertex color is highlighted with the highlight color and the edges connected to that vertex are
Usually displayed in highlight color.
If the other vertex connected to an edge is a selected vertex, the edge is normally displayed in the selection color.
Using this function, you can select vertices to some extent arbitrarily even in places where vertices are complicated.
highlighting
Edges are highlighted with the highlight color when the cursor is over an edge.
However, if the vertices on either end of the edge were selected vertices, they are highlighted instead of changing color.
highlighting
When the cursor is over a face, the face is highlighted with the highlight color.
However, if the vertices on either end of the edge included in the face are selected vertices, they will be highlighted instead of changing color.
highlighting
When the cursor is over a mesh name in Object window, that mesh (or sub-mesh) will be highlighted.
Using this function may increase the machine load, so you can turn it off.
The function OFF button is the button at the bottom of Object window.