Retain labels is actually either a boolean or a number.

src/types/lesser_element.rs

@@ -38,13 +38,21 @@ pub struct CommentBlock<'s> {
 
 pub type CharOffsetInLine = u16;
 
+#[derive(Debug)]
+pub enum RetainLabels {
+    No,
+    Yes,
+    /// When adding -k to the switches on an example or src block, the labels are kept in the source code and links will use line numbers.
+    Keep(CharOffsetInLine),
+}
+
 #[derive(Debug)]
 pub struct ExampleBlock<'s> {
     pub source: &'s str,
     pub name: &'s str,
     pub switches: Option<&'s str>,
     pub number_lines: Option<SwitchNumberLines>,
-    pub retain_labels: Option<CharOffsetInLine>,
+    pub retain_labels: RetainLabels,
     pub use_labels: bool,
     pub label_format: Option<&'s str>,
     pub contents: String,

src/types/mod.rs

@@ -51,6 +51,7 @@ pub use lesser_element::LatexEnvironment;
 pub use lesser_element::LineNumber;
 pub use lesser_element::Paragraph;
 pub use lesser_element::Planning;
+pub use lesser_element::RetainLabels;
 pub use lesser_element::SrcBlock;
 pub use lesser_element::SwitchNumberLines;
 pub use lesser_element::TableCell;