Create API documentation only for user extension (without Yii core) but related with yii2 apidoc (class reference)

[yii-bot]

This issue has originally been reported by @mdmunir at yiisoft/yii2#5612.
Moved here by @cebe.

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How to create api documentation only for my extension (without yii core) but related with yii2 apidoc (class refence)? Good point if can related with http://www.yiiframework.com/doc-2.0/.
When executed like this

./bin/apidoc api mdmsoft/yii2-admin ../admin-apidoc

it will provide error message (errors.txt) "Method ini has no parent to inherit from in mdm\admin\Module".
When executed

./bin/apidoc api mdmsoft/yii2-admin,yiisoft/yii2 ../admin-apidoc

it will generate both of them and index file only list yii2 classes (no mdmsoft classes on index.html)