element: Tiny refactoring

* lisp/org-element.el (org-element-object-restrictions): Use
`minimal-set' to express the common denominator between restrictions.

lisp/org-element.el

@@ -329,7 +329,9 @@ match group 2.
 Don't modify it, set `org-element-affiliated-keywords' instead.")
 
 (defconst org-element-object-restrictions
-  (let* ((standard-set (remq 'table-cell org-element-all-objects))
+  (let* ((minimal-set '(bold code entity italic latex-fragment strike-through
+			     subscript superscript underline verbatim))
+	 (standard-set (remq 'table-cell org-element-all-objects))
 	 (standard-set-no-line-break (remq 'line-break standard-set)))
     `((bold ,@standard-set)
       (footnote-reference ,@standard-set)
@@ -340,23 +342,20 @@ Don't modify it, set `org-element-affiliated-keywords' instead.")
       (keyword ,@(remq 'footnote-reference standard-set))
       ;; Ignore all links in a link description.  Also ignore
       ;; radio-targets and line breaks.
-      (link bold code entity export-snippet inline-babel-call inline-src-block
-	    italic latex-fragment macro statistics-cookie strike-through
-	    subscript superscript underline verbatim)
+      (link export-snippet inline-babel-call inline-src-block macro
+	    statistics-cookie ,@minimal-set)
       (paragraph ,@standard-set)
       ;; Remove any variable object from radio target as it would
       ;; prevent it from being properly recognized.
-      (radio-target bold code entity italic latex-fragment strike-through
-		    subscript superscript underline superscript)
+      (radio-target ,@minimal-set)
       (strike-through ,@standard-set)
       (subscript ,@standard-set)
       (superscript ,@standard-set)
       ;; Ignore inline babel call and inline source block as formulas
       ;; are possible.  Also ignore line breaks and statistics
       ;; cookies.
-      (table-cell bold code entity export-snippet footnote-reference italic
-		  latex-fragment link macro radio-target strike-through
-		  subscript superscript target timestamp underline verbatim)
+      (table-cell export-snippet footnote-reference link macro radio-target
+		  target timestamp ,@minimal-set)
       (table-row table-cell)
       (underline ,@standard-set)
       (verse-block ,@standard-set)))
@@ -366,10 +365,6 @@ key is an element or object type containing objects and value is
 a list of types that can be contained within an element or object
 of such type.
 
-For example, in a `radio-target' object, one can only find
-entities, latex-fragments, subscript, superscript and text
-markup.
-
 This alist also applies to secondary string.  For example, an
 `headline' type element doesn't directly contain objects, but
 still has an entry since one of its properties (`:title') does.")