Only allocate memory if removing text for lesser blocks.

src/types/lesser_element.rs

@@ -1,3 +1,5 @@
+use std::borrow::Cow;
+
 use super::object::Object;
 use super::AffiliatedKeywords;
 use super::GetAffiliatedKeywords;
@@ -59,7 +61,7 @@ pub struct ExampleBlock<'s> {
     pub retain_labels: RetainLabels,
     pub use_labels: bool,
     pub label_format: Option<&'s str>,
-    pub contents: String,
+    pub contents: Cow<'s, str>,
 }
 
 #[derive(Debug)]
@@ -68,7 +70,7 @@ pub struct ExportBlock<'s> {
     pub affiliated_keywords: AffiliatedKeywords<'s>,
     pub export_type: Option<&'s str>,
     pub data: Option<&'s str>,
-    pub contents: String,
+    pub contents: Cow<'s, str>,
 }
 
 #[derive(Debug)]
@@ -83,7 +85,7 @@ pub struct SrcBlock<'s> {
     pub retain_labels: RetainLabels,
     pub use_labels: bool,
     pub label_format: Option<&'s str>,
-    pub contents: String,
+    pub contents: Cow<'s, str>,
 }
 
 #[derive(Debug)]