Create structure for footnote references.

src/parser/object.rs

@@ -18,6 +18,7 @@ pub enum Object<'s> {
     Entity(Entity<'s>),
     LatexFragment(LatexFragment<'s>),
     ExportSnippet(ExportSnippet<'s>),
+    FootnoteReference(FootnoteReference<'s>),
 }
 
 #[derive(Debug, PartialEq)]
@@ -117,6 +118,13 @@ pub struct ExportSnippet<'s> {
     pub contents: Option<&'s str>,
 }
 
+#[derive(Debug, PartialEq)]
+pub struct FootnoteReference<'s> {
+    pub source: &'s str,
+    pub label: &'s str,
+    pub definition: Vec<Object<'s>>,
+}
+
 impl<'s> Source<'s> for Object<'s> {
     fn get_source(&'s self) -> &'s str {
         match self {
@@ -136,6 +144,7 @@ impl<'s> Source<'s> for Object<'s> {
             Object::Entity(obj) => obj.source,
             Object::LatexFragment(obj) => obj.source,
             Object::ExportSnippet(obj) => obj.source,
+            Object::FootnoteReference(obj) => obj.source,
         }
     }
 }
@@ -229,3 +238,9 @@ impl<'s> Source<'s> for ExportSnippet<'s> {
         self.source
     }
 }
+
+impl<'s> Source<'s> for FootnoteReference<'s> {
+    fn get_source(&'s self) -> &'s str {
+        self.source
+    }
+}