If you have multiple components you might end up with a list of those components below each other and your editor do not know which of them. In the screen below the preview would contain the text Hello World! because by default we will use the first field with a string value.

If you want to change which field we use, for example if the field our default system chooses is an image URL you can set the Use for preview radio box inside your fields definition instead.

Once checked the value of this field will be used instead of the default value.

New Feature: We've implemented a feature called Preview Template for all components to further allow you to customize the preview string with even more information and a custom template.