What's "an array of ol.style.Style" good for?

Question

A style of an ol.layer.Vector can be set as ol.style.Style, a style function or an array of ol.style.Style. What's the array for and what does it do -- compared to just passing an ol.style.Style object?

I cannot find any information on this, neither in the official API docs nor in the tutorials.

Answer 1

If you look at the draw features example, when drawing lines, they are displayed in blue with a white border/outline.

These is achieved by styling the line twice, first with a large white line, then a thin blue line above.

There are 2 styles for the same geometry. It can’t be done with a single ol.style.Style, so to achieve this you need to pass an array of 2 styles: see the source for this.