For instance, with bzr 1.12dev (bzr.dev revno:3951), a plugin that requires API version 1.10 produces this backtrace with '-Derror':

cdb@gamma ~/code/bzr/work/bzrlib $ bzr st -Derror
bzr: ERROR: bzrlib.errors.IncompatibleAPI: The API for "<module 'bzrlib' from '/home/cdb/bin/bzr.dev/bzrlib/__init__.pyc'>" is not compatible with "(1, 10, 0)". It supports versions "(1, 11, 0)" to "(1, 12, 0)".

Traceback (most recent call last):
  File "/home/cdb/bin/bzr.dev/bzrlib/commands.py", line 893, in run_bzr_catch_errors
    return run_bzr(argv)
  File "/home/cdb/bin/bzr.dev/bzrlib/commands.py", line 839, in run_bzr
    ret = run(*run_argv)
  File "/home/cdb/.bazaar/plugins/loom/commands.py", line 172, in run_argv_aliases
    self._original_command().run_argv_aliases(argv, alias_argv)
  File "/home/cdb/bin/bzr.dev/bzrlib/commands.py", line 539, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/home/cdb/bin/bzr.dev/bzrlib/commands.py", line 853, in ignore_pipe
    result = func(*args, **kwargs)
  File "/home/cdb/bin/bzr.dev/bzrlib/builtins.py", line 215, in run
    tree, relfile_list = tree_files(file_list)
  File "/home/cdb/bin/bzr.dev/bzrlib/builtins.py", line 64, in tree_files
    return internal_tree_files(file_list, default_branch, canonicalize)
  File "/home/cdb/bin/bzr.dev/bzrlib/builtins.py", line 105, in internal_tree_files
    return WorkingTree.open_containing(default_branch)[0], file_list
  File "/home/cdb/bin/bzr.dev/bzrlib/workingtree.py", line 331, in open_containing
    control, relpath = bzrdir.BzrDir.open_containing(path)
  File "/home/cdb/bin/bzr.dev/bzrlib/bzrdir.py", line 844, in open_containing
    return BzrDir.open_containing_from_transport(transport)
  File "/home/cdb/bin/bzr.dev/bzrlib/bzrdir.py", line 865, in open_containing_from_transport
    result = BzrDir.open_from_transport(a_transport)
  File "/home/cdb/bin/bzr.dev/bzrlib/bzrdir.py", line 819, in open_from_transport
    redirected)
  File "/home/cdb/bin/bzr.dev/bzrlib/lazy_import.py", line 125, in __call__
    return obj(*args, **kwargs)
  File "/home/cdb/bin/bzr.dev/bzrlib/transport/__init__.py", line 1680, in do_catching_redirections
    return action(transport)
  File "/home/cdb/bin/bzr.dev/bzrlib/bzrdir.py", line 806, in find_format
    transport, _server_formats=_server_formats)
  File "/home/cdb/bin/bzr.dev/bzrlib/bzrdir.py", line 1645, in find_format
    return format.probe_transport(transport)
  File "/home/cdb/.bazaar/plugins/svn/format.py", line 71, in probe_transport
    format = klass()
  File "/home/cdb/.bazaar/plugins/svn/format.py", line 61, in __init__
    lazy_check_versions()
  File "/home/cdb/.bazaar/plugins/svn/__init__.py", line 137, in lazy_check_versions
    bzrlib.api.require_any_api(bzrlib, COMPATIBLE_BZR_VERSIONS)
  File "/home/cdb/bin/bzr.dev/bzrlib/api.py", line 104, in require_any_api
    require_api(object_with_api, wanted_api_list[-1])
  File "/home/cdb/bin/bzr.dev/bzrlib/api.py", line 82, in require_api
    raise IncompatibleAPI(object_with_api, wanted_api, minimum, current)
IncompatibleAPI: The API for "<module 'bzrlib' from '/home/cdb/bin/bzr.dev/bzrlib/__init__.pyc'>" is not compatible with "(1, 10, 0)". It supports versions "(1, 11, 0)" to "(1, 12, 0)".