Fixing some errors reported by the CI.

Author: Mbodin

lib/svg_sigs.mli

@@ -1116,6 +1116,8 @@ module type Wrapped_functions = sig
   val string_of_orient : (Svg_types.Unit.angle option, string) Xml.W.ft
 
   val string_of_paint : ([< Svg_types.paint], string) Xml.W.ft
+
+  val string_of_opacity : (float, string) Xml.W.ft
 
   val string_of_fill_rule : ([< Svg_types.fill_rule], string) Xml.W.ft
 

syntax/attribute_value.ml

@@ -501,12 +501,12 @@ let fill_opacity =
       in
 
       let v =
-        if group_matched 2 s then [%expr [%e n] /. 100.]
-        else [%expr [%e n]] in
+        if group_matched 2 s then ([%e n] /. 100.)
+        else [%e n] in
 
-      if v >= 0. && v <= 1. then Some v
+      if v >= 0. && v <= 1. then Some [%expr v]
       else
-        Common.error loc "Value of %s must be between 0 and 1." name in
+        Common.error loc "Value of %s must be between 0 and 1." name
     end [@metaloc loc]
 
 let fill_rule ?separated_by:_ ?default:_ loc _name s =