src/vs/editor/browser/services/abstractCodeEditorService.ts/DecorationSubTypeOptionsProvider/getOptions
class DecorationSubTypeOptionsProvider:	public getOptions(codeEditorService: AbstractCodeEditorService, writable: boolean): IModelDecorationOptions {
		const options = codeEditorService.resolveDecorationOptions(this._parentTypeKey, true);
		if (this._beforeContentRules) {
			options.beforeContentClassName = this._beforeContentRules.className;
		}
		if (this._afterContentRules) {
			options.afterContentClassName = this._afterContentRules.className;
		}
		return options;
	}