first import

sites/all/modules/openlayers/docs/IE.txt

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+
+Using the OpenLayers Javascript from the OpenLayers module can present some
+problems with rendering vector layers in IE.
+
+The root cause of the issue:
+
+Internet Explorer has a thing called VML: Vector Markup Language, which it uses
+to draw graphics. VML is what you use in IE: canvas4ie is way slow, google maps
+uses VML to draw routes, and OpenLayers uses it to draw vectors.
+
+VML elements are styled by creating CSS-like styles in a namespace. OpenLayers
+creates an ol: namespace and then creates styles like ol:line ol:circle, etc.
+
+To do this, it has to access document.namespaces. Document.namespaces is not
+always around: notably, you can't depend on it being around before
+document.ready.
+
+But, sometimes document.namespaces *is* around before document.ready and that's
+the thing that messed up my worldview. So, the theory was, there are modes.
+Something in HTML can prevent document.namespaces being filled in before
+document.ready.
+
+Here's how it goes.
+
+### $( or $(document).ready()
+
+* If there is a broken image on the page, then namespaces is not filled in.
+* If the page has no broken images, then document.namespaces is accessible
+
+### document.load()
+
+* document.namespaces is always filled in.
+
+### 31 stylesheets
+
+IE cannot handle more than 31 stylesheets on a page at a time. This is clearly
+the devil's work, but it persists beyond IE8. If there are 31 stylesheets and
+you run an OpenLayers map, it cannot add another stylesheet to initialize its
+VML namespace. Therefore, the map breaks. You must aggregate your CSS.
+
+### The Fix
+
+We can't move openlayers to document.load() because it is dependent on the
+Drupal behaviors stack, that runs on document.ready(). We need to just define
+document.namespaces before OpenLayers asks its VML renderer whether the current
+browser is capable of rendering VML (a task it tries to complete by calling
+!!(document.namespaces))
+
+### Other Fixes
+
+Adding a tag
+<code><meta http-equiv="X-UA-Compatible" content="IE=EmulateIE7" /></code>
+will allow IE8 to render vectors if it doesn't render them correctly on a normal
+pageload. Note that this must be the first element inside the header tag.
+
+### Image Opacity
+
+The opacity of image pointers are created with IE filters, which do not function
+correctly when combined with semi-transparent PNG images. Thus it is necessary
+to set opacity of such elements to 1.0 in order for alpha-transparent PNG images
+to appear correctly.