Make block from a multi-layer drawing when objects are not on Layer 0

I want to create a block from a drawing, but since I am already using layers,
the drawing I wish to convert into a block is not on Layer 0 as the documentation
suggests. What should I do?

https://docs.librecad.org/en/2.2.0_a/guides/blocks.html#creating-a-block

1. Ensure the all entities for the object to be made into a block are on layer “0”.

Move or copy.

Removing the Layer 0  requirement would be an useful improvement.

Have tried selecting objects, copying them and pasting them in another document
at Layer 0.  But the pasting is not executing.

Heime wrote

Removing the Layer 0  requirement would be an useful improvement.

As you mentioned in your opening post, it is a suggestion not a requirement. Thus, nothing to remove.

The recommendation in the manual is based on the author's experience and surely advisable when creating blocks for libraries to share.

It is impossible to document and explain each feature or reason its functionality.
As with every other software too, there is always more than one way to achieve a goal. Some ways are intended, others by chance.
Which way is the best depends on personal experience, taste or given requirements.
With a certain level of trial-and-error find out what fits best for you.

I use blocks with layers myself if it is needed. So give it a go and if you get in trouble, you have learned when it is okay to have layers in a block and when to avoid it.
There is no general rule I can share with you, there are so many use cases and possibilities.

It would be helpful if the manual clarified that using Layer 0 is not mandatory.

The word "Ensure" should be removed because it is misleading, implying that it is
the only acceptable method.  Additionally, the grammar in the original statement
is incorrect, which suggests that it was not carefully considered.

Current documentation excerpt:

Creating a Block - Ensure the all entities for the object to be made into a block are on layer "0".

How does one select a set of objects and make a block from them?  

Have selected the objects I need and copied them, then pressed  the Create Block
icon from the Block List.  But Create Block does nothing.

When I do Edit the active block in a separate window I thought that all drawing
elements would be grouped together.  But I still can select them separately.  I thought
that all elements would be grouped together and I would need to execute Explode.