Unable to find API for setting outline level

This may sound foolish, but I have searched through the documentation and cannot find the API for setting the outline level. Could you please help me find it

Hello @nichaoshou

Please specify what you want to outline in the first place.

May I ask if there is an API for setting the outline level

There are lots of elements that inherit their own way of setting outline levels.
For example, outline level for a text passage in the run can be set via these methods:

For even more examples, here are several methods to outline elements of a chart:

As you can see there are plenty of elements to set outline for, that is why I asked what do you want to outline exactly and where, with this information I can find a suitable for you method.

What I want to achieve is to create an outline level for my custom style in the plugin, as shown in the picture

Thanks for clarifying.
I am looking for the needed method, once I find anything I’ll let you know.