def value(val, transform=None):
    """ Convenience function to explicitly return a "value" specification for
    a Bokeh :class:`~bokeh.core.properties.DataSpec` property.

    Args:
        val (any) : a fixed value to specify for a ``DataSpec`` property.

        transform (Transform, optional) : a transform to apply (default: None)

    Returns:
        dict : ``{ "value": name }``

    .. note::
        String values for property specifications are by default interpreted
        as field names. This function is especially useful when you want to
        specify a fixed value with text properties.

    Example:

        .. code-block:: python

            # The following will take text values to render from a data source
            # column "text_column", but use a fixed value "16px" for font size
            p.text("x", "y", text="text_column",
                   text_font_size=value("16px"), source=source)

    """
    if transform:
        return dict(value=val, transform=transform)
    return dict(value=val)