There have been some changes between versions ~1.0 and ~4.0. Foremost is that the new BootstrapComponents utilizes Twitter Bootstrap4. Therefore, it mirrors changes made by Bootstrap.

Also, extension loading must now be done manually in your LocalSettings, no matter whether you installed it via composer or manually.

BootstrapComponents now has to loaded manually, whether you installed it via composer or by cloning it from github. Just add the following to your LocalSettings.php file:

wfLoadExtension( 'BootstrapComponents' );

There have been some changes in the components provided by Bootstrap4 and the ExtensionBootstrap. Some of them unfortunately need your attention.

This is the change with the severest impact: the glyphicon font has been removed. BootstrapComponents unfortunately cannot provide a suitable replacement. If you need fancy items, please have a look at Extension:FontAwesome.

The Label component has been removed, its functionality is now provided by the Badge Component. BootstrapComponents takes care of that by having the label component inside your wiki text rendered with bootstrap4's badge attributes and classes.

In other words, you can use these two elements in your wiki and they both produce the same output:

{{#bootstrap_label: text | .. }}
{{#bootstrap_badge: text | .. }}

However, it is recommended that on new pages or new edits you now only use the badge component.

Bootstrap4 removes the Panel and the Well and introduces the new component Card. Since "Bootstrap’s cards provide a flexible and extensible content container with multiple variants and options." it can be used to render things to look like Panels and Wells. Again, BootstrapComponents takes care of that by rendering a Well and a Panel like a Bootstrap4 Card.

Subsequently, these calls all produce the same output:

<bootstrap_card [..]>Content text for the box</bootstrap_card>
<bootstrap_panel [..]>Content text for the box</bootstrap_panel>
<bootstrap_well [..]>Content text for the box</bootstrap_well>

This includes panels inside accordions, as well.

Again, it is recommended that on new pages or new edits you now only use the card component.