The TkPane Python Libary
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This library (*tkpane.py*) simplifies the development of Tkinter user
interfaces and the specification of interactions between UI elements.

A base class (TkPane) is defined that is meant to be subclassed to
create 'pane' objects that have no inherent dependencies on other
UI elements (panes or widgets).

After subclass objects are instantiated, interactions between them
can be defined through well-defined interface functions that implement
actions to enable, clear, or disable the panes; callback lists that
are activated when data become valid or invalid, and a set of methods
that automatically establish certain types of relationships between
panes.  For example, the ``requires()`` methd is used like this:

    pane_b.requires(pane_a)

to ensure that ``pane_b`` will be enabled when ``pane_a`` has valid
data, and will be disabled when ``pane_a`` has invalid data.

Full documentation is available at http://tkpane.readthedocs.io
