Implement parser for subscript/superscript with braces.

src/parser/parser_context.rs

@@ -194,6 +194,18 @@ pub enum ContextElement<'r, 's> {
     /// unbalanced brackets can be detected in the middle of an
     /// object.
     InlineSourceBlockBracket(InlineSourceBlockBracket<'s>),
+
+    /// Stores the current bracket or parenthesis depth inside a
+    /// superscript or superscript.
+    ///
+    /// Inside the braces of a subscript or superscript there must be
+    /// balanced braces {}, so this stores the amount of opening
+    /// braces subtracted by the amount of closing braces within the
+    /// definition must equal zero.
+    ///
+    /// A reference to the position in the string is also included so
+    /// unbalanced braces can be detected in the middle of an object.
+    SubscriptSuperscriptBrace(SubscriptSuperscriptBrace<'s>),
 }
 
 pub struct ExitMatcherNode<'r> {
@@ -225,6 +237,12 @@ pub struct InlineSourceBlockBracket<'s> {
     pub depth: usize,
 }
 
+#[derive(Debug)]
+pub struct SubscriptSuperscriptBrace<'s> {
+    pub position: &'s str,
+    pub depth: usize,
+}
+
 impl<'r> std::fmt::Debug for ExitMatcherNode<'r> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         let mut formatter = f.debug_struct("ExitMatcherNode");