Workaround for #134.

Gave up on finding a real fix for #134, so documenting a workaround
instead.

examples/warp03/templates/intermediate.rs.html

@@ -1,7 +1,7 @@
 @use super::base_html;
 
 @(title: &str, htmlargs: Content, content: Content)
-@:base_html(title, htmlargs, {
+@:base_html(title, {@:htmlargs()}, {
   @:content()
   <p>This whole site is an example.</p>
 })

src/Template_syntax.rs

@@ -301,4 +301,26 @@ pub mod d_Calling_other_templates {
     //!     <p>page content ...</p>
     //! })
     //! ```
+    //!
+    //! ## Intermediate templates with block parameters
+    //!
+    //! Due to a limitation in Ructe, it is currently not possible to
+    //! take a block parameter and send directly along to further
+    //! templates.
+    //! The following will not work:
+    //!
+    //! ```compile_fail
+    //! @(title: &str, body: Content) {{
+    //!   @:base_page_html(title, body)
+    //! }}
+    //! ```
+    //!
+    //! Instead, the parameter needs to be a block, even if only to
+    //! call the existing one:
+    //!
+    //! ```text
+    //! @(title: &str, body: Content) {{
+    //!   @:base_page_html(title, {@:body()})
+    //! }}
+    //! ```
 }