Index: class.doc
==================================================================
--- class.doc
+++ class.doc
@@ -2261,10 +2261,28 @@
   Display a unsigned hexadecimal number in uppercase.
 
 %%
   Display a percentage sign; does not consume an argument.
 
+%(
+  Begin a conditional block, of the form "%(true-part%|false-part%)" or
+  "%(true-part%)". Consumes one argument; if zero then the false-part is
+  used (or nothing, if there is no false-part), or if nonzero then the
+  true-part is used. Conditional blocks cannot be nested.
+
+%|
+  Else part of a conditional block. See above about conditional blocks.
+
+%)
+  End of a conditional block. See above about conditional blocks.
+
+%<
+  Unconsume one argument. (Does not produce any output.)
+
+%>
+  Skip one argument. (Does not produce any output.)
+
 
 === Messages ===
 
 This section describes when the various standard messages are sent to
 objects, and what return values are expected. (Do not confuse CREATE with

Index: exec.c
==================================================================
--- exec.c
+++ exec.c
@@ -2076,10 +2076,33 @@
             if(v.t==TY_NUMBER) sqlite3_str_appendf(s,"%X",(unsigned int)v.u);
             break;
           case '%':
             sqlite3_str_appendchar(s,1,'%');
             break;
+          case '(':
+            if(argi==argc) break;
+            v=vstack[vstackptr+argi++];
+            if(v.t || v.u) break;
+            // otherwise fall through
+          case '|':
+            while(u=strchr(t,'%')) {
+              t=u+(u[1]?2:1);
+              if(u[1]==')' || u[1]=='|') break;
+            }
+            break;
+          case ')':
+            // no effect
+            break;
+          case '<':
+            if(argi>0) --argi;
+            break;
+          case '>':
+            if(argi<argc) ++argi;
+            break;
+          default:
+            if(main_options['t'] || main_options['v']) fprintf(stderr,"Unrecognized %% code in (PopUp)\n");
+            break;
         }
       } else {
         sqlite3_str_appendall(s,t);
         break;
       }