Add tests for broken export blocks.

org_mode_samples/lesser_block/export_with_no_data.org

@@ -0,0 +1,3 @@
+#+begin_export
+This would be LaTeX code.
+#+end_export

org_mode_samples/lesser_block/export_with_two_words.org

@@ -0,0 +1,3 @@
+#+begin_export latex html
+This would be LaTeX code.
+#+end_export

src/parser/lesser_block.rs

@@ -173,7 +173,7 @@ pub fn export_block<'r, 's>(
     input: &'s str,
 ) -> Res<&'s str, ExportBlock<'s>> {
     let (remaining, name) = lesser_block_begin("export")(context, input)?;
-    // TODO: Data is mandatory and must be a single word
+    // https://orgmode.org/worg/org-syntax.html#Blocks claims that export blocks must have a single word for data but testing shows no data and multi-word data still parses as an export block.
     let (remaining, parameters) = opt(tuple((space1, data)))(remaining)?;
     let (remaining, _nl) = line_ending(remaining)?;
     let lesser_block_end_specialized = lesser_block_end("export");