Add support for babel-call keywords.

src/types/element.rs

@@ -44,6 +44,7 @@ pub enum Element<'s> {
     FixedWidthArea(FixedWidthArea<'s>),
     HorizontalRule(HorizontalRule<'s>),
     Keyword(Keyword<'s>),
+    BabelCall(Keyword<'s>),
     LatexEnvironment(LatexEnvironment<'s>),
 }
 
@@ -70,6 +71,7 @@ impl<'s> Source<'s> for Element<'s> {
             Element::FixedWidthArea(obj) => obj.source,
             Element::HorizontalRule(obj) => obj.source,
             Element::Keyword(obj) => obj.source,
+            Element::BabelCall(obj) => obj.source,
             Element::LatexEnvironment(obj) => obj.source,
         }
     }
@@ -99,6 +101,7 @@ impl<'s> SetSource<'s> for Element<'s> {
             Element::FixedWidthArea(obj) => obj.source = source,
             Element::HorizontalRule(obj) => obj.source = source,
             Element::Keyword(obj) => obj.source = source,
+            Element::BabelCall(obj) => obj.source = source,
             Element::LatexEnvironment(obj) => obj.source = source,
         }
     }