def edit(text=None, editor=None, env=None, require_save=True, extension=
    '.txt', filename=None):
    """Edits the given text in the defined editor.  If an editor is given
    (should be the full path to the executable but the regular operating
    system search path is used for finding the executable) it overrides
    the detected editor.  Optionally, some environment variables can be
    used.  If the editor is closed without changes, `None` is returned.  In
    case a file is edited directly the return value is always `None` and
    `require_save` and `extension` are ignored.

    If the editor cannot be opened a :exc:`UsageError` is raised.

    Note for Windows: to simplify cross-platform usage, the newlines are
    automatically converted from POSIX to Windows and vice versa.  As such,
    the message here will have ``\\n`` as newline markers.

    :param text: the text to edit.
    :param editor: optionally the editor to use.  Defaults to automatic
                   detection.
    :param env: environment variables to forward to the editor.
    :param require_save: if this is true, then not saving in the editor
                         will make the return value become `None`.
    :param extension: the extension to tell the editor about.  This defaults
                      to `.txt` but changing this might change syntax
                      highlighting.
    :param filename: if provided it will edit this file instead of the
                     provided text contents.  It will not use a temporary
                     file as an indirection in that case.
    """
    from ._termui_impl import Editor
    editor = Editor(editor=editor, env=env, require_save=require_save,
        extension=extension)
    if filename is None:
        return editor.edit(text)
    editor.edit_file(filename)
