[docs] Stage introspection: up

docs/pages/reference/development_and_debug/stage_introspection.md

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-Writing a configuration is especially difficult at the beginning because you don't quite understand what is in the _stage assembly container_ when the instructions are executed.
+Writing a configuration is especially difficult at the beginning because you do not quite understand what is in the _stage assembly container_ when the instructions are executed.
 
 In the process of assembling, you can access a certain _stage_ using introspection options. During introspection, like during assembling, the _stage assembly container_ contains service tools and environment variables. Tools are presented as a set of utilities required during assembling. They are added by mounting the directories from service containers of our _stapel_ distributions (available at `/.werf/stapel` path in the _assembly container_). Introspection comes down the fact that the _stage assembly container_ is launched for users in interactive mode.
 
+The `--introspect-stage` option can be used multiple times to introspect several stages. There are the following formats to use:
+
+* specify `IMAGE_NAME/STAGE_NAME` to introspect stage `STAGE_NAME` of either **image or artifact** `IMAGE_NAME`. The nameless image can be defined by `~`.;
+* specify `STAGE_NAME` or `*/STAGE_NAME` for the introspection of all existing stages with name `STAGE_NAME`.
+
 **During development**, introspection makes it possible to achieve the required outcomes in an _assembly container_, and then transfer all the steps and instructions into the configuration of the appropriate _stage_. This approach is useful when the set objective is clear, although the steps to achieve it are not so obvious and require a great deal of experiment.
 
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