use an assign to capture platform string

modules/binarization.md

@@ -85,20 +85,21 @@ Open an image and binarize it by applying a threshold.
   {% assign first = true %}
 {% endif %}
 {% for platform in page.platforms %}
+  {% assign platstring = platform[0] %}
   {% if first %}
-    <option value="{{platform[0]}}" id="{{platform[0]}}" selected="selected"> {{platform[0]}} </option>
+    <option value="{{platstring}}" id="{{platstring}}" selected="selected"> {{platstring}} </option>
 
     {% assign first = false %}
   {% else %}
-    <option value="{{platform[0]}}" id="{{platform[0]}}"> {{platform[0]}} </option>
+    <option value="{{platstring}}" id="{{platstring}}"> {{platstring}} </option>
   {% endif %}
 {% endfor %}
 {% if page.platforms %}
   </select>
 {% endif %}
 {% for platform in page.platforms %}
-  <div id="{{platform[0]}}">
-    <h4>{{platform[0]}}</h4>
+  <div id="{{platstring}}">
+    <h4>{{platstring]}}</h4>
     {% assign includefile = platform[1] %}
     {% capture my_include %}{% include {{includefile}} %}{% endcapture %}