add support for number signs +-

cms/static/grammar.jspeg

@@ -111,11 +111,11 @@ primary
   / "(" additive:additive ")" { return additive; }
 
 decimal "decimal"
-  = first:[0-9]+ point:'.' last:[0-9]+
-    { return parseFloat(first.join("") + point + last.join("")); }
+  = sign:[+-]? first:[0-9]* point:'.' last:[0-9]+
+    { return parseFloat(sign + first.join("") + point + last.join("")); }
 
 integer "integer"
-  = digits:[0-9]+ { return parseInt(digits.join(""), 10); }
+  = sign:[+-]? digits:[0-9]+ { return parseInt(sign + digits.join(""), 10); }
 
 percentage "percentage"
   = digits:[0-9]+ '%' { return parseInt(digits.join(""), 10) + '%'; }
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