documentation update

src/commands.hxx

@@ -1915,7 +1915,15 @@ class Set: public Command {
         " output, such as <do>, which returns the result of JavaScript or"
         " <execute>, which returns the output of the executed command, or"
         " <call>, which returns the result of the last command."
-        " All variables are global with regard to functions.";
+        " All variables are global with regard to functions.\n\n"
+        "To set a variable to the value of an input field, you can use:\n\n"
+        "  "+tag()+" <variable>\n"
+        "    do <selector>\n"
+        "      this.value\n\n";
+        "To set a variable to the inner html content of an element, you can use:\n\n"
+        "  "+tag()+" <variable>\n"
+        "    do <selector>\n"
+        "      this.innerHTML";
     }
     QString command() const {
       if (_next)