clarified NEWS: document_files are officially required since Isabelle2014, but the absence was tolerated as legacy feature;
section \<open>Concrete Syntax\<close>
theory Quote_Antiquote imports Main begin
syntax
"_quote" :: "'b \<Rightarrow> ('a \<Rightarrow> 'b)" ("(\<guillemotleft>_\<guillemotright>)" [0] 1000)
"_antiquote" :: "('a \<Rightarrow> 'b) \<Rightarrow> 'b" ("\<acute>_" [1000] 1000)
"_Assert" :: "'a \<Rightarrow> 'a set" ("(\<lbrace>_\<rbrace>)" [0] 1000)
translations
"\<lbrace>b\<rbrace>" \<rightharpoonup> "CONST Collect \<guillemotleft>b\<guillemotright>"
parse_translation \<open>
let
fun quote_tr [t] = Syntax_Trans.quote_tr @{syntax_const "_antiquote"} t
| quote_tr ts = raise TERM ("quote_tr", ts);
in [(@{syntax_const "_quote"}, K quote_tr)] end
\<close>
end