Explain evaluator option syntax for value_ text antiquotation

examples/technical_report/Isabelle_DOF-Manual/04_RefMan.thy

@@ -338,7 +338,7 @@ is currently only available in the SML API's of the kernel.
         | @@{command "ML*"}   ('[' meta_args ']')? '\<open>' SML_code '\<close>'
         | @@{command "term*"} ('[' meta_args ']')? '\<open>' HOL_term  '\<close>'
         | (@@{command "value*"} 
-          | @@{command "assert*"}) \<newline> ('[' meta_args ']' ('[' evaluator ']')?)? '\<open>' HOL_term '\<close>'
+          | @@{command "assert*"}) \<newline> ('[' meta_args ']')? ('[' evaluator ']')? '\<open>' HOL_term '\<close>'
     )
   \<close>
 \<^rail>\<open>  

src/tests/Evaluation.thy

@@ -207,4 +207,8 @@ text\<open>... and here we reference @{A [display] \<open>assertionA\<close>}.\<
 
 assert*\<open>evidence @{result \<open>resultProof\<close>} = evidence @{result \<open>resultProof2\<close>}\<close>
 
+text\<open>The optional evaluator of \<open>value*\<close> and \<open>assert*\<close> must be specified before the meta arguments:\<close>
+value* [optional_test_A::A, x=6] [nbe] \<open>filter (\<lambda>\<sigma>. A.x \<sigma> > 5) @{A-instances}\<close>
+assert* [resultProof3::result, evidence = "proof", property="[@{thm \<open>HOL.sym\<close>}]"] [nbe]
+        \<open>evidence @{result \<open>resultProof3\<close>} = evidence @{result \<open>resultProof2\<close>}\<close>
 end

src/tests/TermAntiquotations.thy

@@ -116,6 +116,12 @@ text\<open>Terms containing term antiquotations can be checked and evaluated
 using \<^theory_text>\<open>term_\<close> and \<^theory_text>\<open>value_\<close> text antiquotations respectively:
 We can print the term @{term_ \<open>r @{F \<open>xcv4\<close>}\<close>} with \<open>@{term_ \<open>r @{F \<open>xcv4\<close>}\<close>}\<close>
 or get the value of the \<^const>\<open>F.r\<close> attribute of @{docitem \<open>xcv4\<close>} with \<open>@{value_ \<open>r @{F \<open>xcv4\<close>}\<close>}\<close>
+\<^theory_text>\<open>value_\<close> may have an optional argument between square brackets to specify the evaluator but this
+argument must be specified after a default optional argument already defined
+by the text antiquotation implementation.
+So one must use the following syntax if he does not want to specify the first optional argument:
+\<open>@{value_ [] [nbe] \<open>r @{F \<open>xcv4\<close>}\<close>}\<close>. Note the empty brackets.
+
 \<close>
 
 text\<open>There also are \<^theory_text>\<open>term_\<close> and \<^theory_text>\<open>value_\<close> ML antiquotations: