class_opt,

                    text_spec,

                let text_spec = match graphic_spec.class_opt {
                    Some(GraphicClass::Cleaned)     => TextSpec::Link,
                    Some(GraphicClass::Collated)    => TextSpec::Link,
                    Some(GraphicClass::Source)      => TextSpec::Meta,
                    // Default is assumed implicitly to be GraphicClass::Source.
                    None                            => TextSpec::Meta,
                };

                    text_spec:  graphic_spec.text_spec,

                    text_spec:  text_spec, 

    }
}
#[derive(Debug)]
pub enum GraphicClass {
    /// Generally the top graphic which displays all time-series. 
    Collated,
    /// A single time-series which displays un-transformed data directly from source.
    Source,
    /// Data that has been selected and transformed.
    Cleaned,
}
impl FromStr for GraphicClass {
    type Err = Error;
    fn from_str(s: &str) -> Result<Self, Error> {
        match s {
            "collated"  => Ok(GraphicClass::Collated),
            "source"    => Ok(GraphicClass::Source),
            "cleaned"   => Ok(GraphicClass::Cleaned),
            _           => Err(keytree_error(file!(), line!(), "Failed to parse GraphicClass")),
        }

impl fmt::Display for GraphicClass {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let s = match self {
            GraphicClass::Collated  => "collated",
            GraphicClass::Source    => "source",
            GraphicClass::Cleaned   => "cleaned",
        };
        write!(f, "{}", s)
    }
}

    pub class_opt:  Option<GraphicClass>,

    pub text_spec:  TextSpec,

                class_opt:      self.opt_value("graphic::class")?,

                text_spec:      self.value("graphic::text")?,

        if let Some(class) = &self.class_opt {
            kt.push_value(1, "class", class);
        }

        kt.push_value(1, "text", &self.text_spec);

    GraphicClass,

                class_opt:  Some(GraphicClass::Collated),

                text_spec:  TextSpec::Link,

                    class_opt:  Some(GraphicClass::Source),

                    text_spec:  TextSpec::Meta,