Implement the parser for inline babel calls.

src/parser/parser_context.rs

@@ -168,6 +168,19 @@ pub enum ContextElement<'r, 's> {
     /// unbalanced brackets can be detected in the middle of an
     /// object.
     CitationBracket(CitationBracket<'s>),
+
+    /// Stores the current bracket or parenthesis depth inside an inline babel call.
+    ///
+    /// Inside an inline babel call the headers must have balanced
+    /// parentheses () and the arguments must have balanced brackets
+    /// [], so this stores the amount of opening brackets subtracted
+    /// by the amount of closing brackets within the definition must
+    /// equal zero.
+    ///
+    /// A reference to the position in the string is also included so
+    /// unbalanced brackets can be detected in the middle of an
+    /// object.
+    BabelHeaderBracket(BabelHeaderBracket<'s>),
 }
 
 pub struct ExitMatcherNode<'r> {
@@ -187,6 +200,12 @@ pub struct CitationBracket<'s> {
     pub depth: usize,
 }
 
+#[derive(Debug)]
+pub struct BabelHeaderBracket<'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");