Set up code structure for lesser blocks.

src/compare/diff.rs

@@ -9,6 +9,7 @@ use crate::parser::Element;
 use crate::parser::FootnoteDefinition;
 use crate::parser::GreaterBlock;
 use crate::parser::Heading;
+use crate::parser::LesserBlock;
 use crate::parser::Paragraph;
 use crate::parser::PlainList;
 use crate::parser::PlainListItem;
@@ -202,6 +203,7 @@ fn compare_element<'s>(
         Element::Drawer(obj) => compare_drawer(source, emacs, obj),
         Element::PropertyDrawer(obj) => compare_property_drawer(source, emacs, obj),
         Element::Table(obj) => compare_table(source, emacs, obj),
+        Element::LesserBlock(obj) => compare_lesser_block(source, emacs, obj),
     }
 }
 
@@ -548,3 +550,11 @@ fn compare_table_cell<'s>(
         children: child_status,
     })
 }
+
+fn compare_lesser_block<'s>(
+    source: &'s str,
+    emacs: &'s Token<'s>,
+    rust: &'s LesserBlock<'s>,
+) -> Result<DiffResult, Box<dyn std::error::Error>> {
+    todo!()
+}