Is vkCmdExecuteCommands "dynamic"?

[JoshKlint]

Is vkCmdExecuteCommands() a way to specify a command buffer that can be dynamically modified, or is it just a way of adding the contents of one command buffer to another?

In other words:
Record secondary command buffer A
Record primary command buffer B, including vkCmdExecuteCommands to execute A.
Modify A.
Execute B, and the modified contents of A are executed.

[krOoze]

@JoshKlint

Is vkCmdExecuteCommands() a way to specify a command buffer that can be dynamically modified, or is it just a way of adding the contents of one command buffer to another?

The later:                                

@The Specification

If a secondary moves to any other state whilst it is recorded to another command buffer, the primary moves to the invalid state.