replace markdown in doxygen with html to support older versions

doc/mainpage.dox

@@ -9,62 +9,63 @@ events (such as data changes) can be negotiated with the server. The client/serv
 mapped either to a binary encoding and TCP-based transmission or to SOAP-based webservices. As of
 late, OPC UA is marketed as the one standard for non-realtime industrial communication.
 
-We believe that it is best to understand OPC UA *from the inside out*, building upon conceptually
+We believe that it is best to understand OPC UA <em>from the inside out</em>, building upon conceptually
 simple first principles. After establishing a first understanding, we go on explaining how these
-principles are realized in detail. Examples are given based on the *open62541* implementation of the
+principles are realized in detail. Examples are given based on the </em>open62541</em> implementation of the
 standard.
 
-OPC UA, a collection of services
---------------------------------
+<h2>OPC UA, a collection of services</h2>
 
 In OPC-UA, all communication is based on service calls, each consisting of a request and a response
 message. Be careful to note the difference between services and methods. Services are pre-defined in
-the standard and cannot be changed. But you can use the *Call* service to invoke user-defined
+the standard and cannot be changed. But you can use the <em>Call</em> service to invoke user-defined
 methods on the server.
 
 For completeness, the following tables contain all services defined in the standard. Do not bother
 with their details, yet. We will introduce the different services later in the text. In open62541,
 each service is implemented in a single function. See the \ref services section for details.
 
-__Establishing communication__
+<bf>Establishing communication</bf>
 
-| Discovery Service Set | SecureChannel Service Set | Session Service Set |
-|-----------------------|---------------------------|---------------------|
-| FindServers           | OpenSecureChannel         | CreateSession       |
-| GetEndpoints          | CloseSecureChannel        | ActivateSession     |
-| RegisterServer        |                           | CloseSession        |
-|                       |                           | Cancel              |
-
-__Interaction with the information model__
+<table>
+<tr> <th>Discovery Service Set </th><th>SecureChannel Service Set </th><th>Session Service Set </th></tr>
+<tr> <td>FindServers </td><td>OpenSecureChannel </td><td>CreateSession </td></tr>
+<tr> <td>GetEndpoints </td><td>CloseSecureChannel </td><td>ActivateSession </td></tr>
+<tr> <td>RegisterServer </td><td></td><td>CloseSession </td></tr>
+<tr> <td></td><td></td><td>Cancel </td></tr>
+</table>
 
-| NodeManagement Service Set | View Service Set               | Query Service Set | Attribute Service Set | Method Service Set |
-|----------------------------|--------------------------------|-------------------|-----------------------|--------------------|
-| AddNodes                   | Browse                         | QueryFirst        | Read                  | Call               |
-| AddReferences              | BrowseNext                     | QueryNext         | HistoryRead           |                    |
-| DeleteNodes                | TranslateBrowsePathsToNodeIds  |                   | Write                 |                    |
-| DeleteReferences           | RegisterNodes                  |                   | HistoryUpdate         |                    |
-|                            | UnregisterNodes                |                   |                       |                    |
+<bf>Interaction with the information model</bf>
 
-__Notifications__
+<table>
+<tr> <th>NodeManagement Service Set </th><th>View Service Set </th><th>Query Service Set </th><th>Attribute Service Set </th><th>Method Service Set  </th></tr>
+<tr> <td>AddNodes </td><td>Browse </td><td>QueryFirst </td><td>Read </td><td>Call </td></tr>
+<tr> <td>AddReferences </td><td>BrowseNext </td><td>QueryNext </td><td>HistoryRead </td><td></td></tr>
+<tr> <td>DeleteNodes </td><td>TranslateBrowsePathsToNodeIds </td><td></td><td>Write </td><td></td></tr>
+<tr> <td>DeleteReferences </td><td>RegisterNodes </td><td></td><td>HistoryUpdate </td><td></td></tr>
+<tr> <td></td><td>UnregisterNodes </td><td></td><td></td><td></td></tr>
+</table>
 
-| MonitoredItem Service Set | Subscription Service Set |
-|---------------------------|--------------------------|
-| CreateMonitoredItems      | CreateSubscription       |
-| ModifyMonitoredItems      | ModifySubscription       |
-| SetMonitoringMode         | SetPublishingMode        |
-| SetTriggering             | Publish                  |
-| DeleteMonitoredItems      | Republish                |
-|                           | TransferSubscription     |
-|                           | DeleteSubscription       |
+<bf>Notifications</bf>
 
+<table>
+<tr> <th>MonitoredItem Service Set </th><th>Subscription Service Set  </th></tr>
+<tr> <td>CreateMonitoredItems </td><td>CreateSubscription </td></tr>
+<tr> <td>ModifyMonitoredItems </td><td>ModifySubscription </td></tr>
+<tr> <td>SetMonitoringMode </td><td>SetPublishingMode </td></tr>
+<tr> <td>SetTriggering </td><td>Publish </td></tr>
+<tr> <td>DeleteMonitoredItems </td><td>Republish </td></tr>
+<tr> <td></td><td>TransferSubscription </td></tr>
+<tr> <td></td><td>DeleteSubscription </td></tr>
+</table>
 
 OPC UA, a web of nodes
 ----------------------
 
 The information model in each OPC UA server is a web of interconnected nodes. There are eight
 different types of nodes. Depending on its type, every node contains different attributes. Some
-attributes, such as the *NodeId* (unique identifier) and the *BrowseName*, are contained in all node
-types.
+attributes, such as the <em>NodeId</em> (unique identifier) and the <em>BrowseName</em>, are
+contained in all node types.
 
 <table>
 <tr> <td>ReferenceTypeNode</td> <td>MethodNode</td> </tr>
@@ -73,8 +74,8 @@ types.
 <tr> <td>VariableNode</td> <td>ViewNode</td> </tr>
 </table>
                                                                                                             
-Nodes are interconnected by directed reference-triples of the form `(nodeid, referencetype,
-target-nodeid)`. Therefore an OPC UA information model is easiest imagined as a __web of nodes__.
+Nodes are interconnected by directed reference-triples of the form <dfn>(nodeid, referencetype,
+target-nodeid)</dfn>. Therefore an OPC UA information model is easiest imagined as a <em>web of nodes</em>.
 Reference types can be
 - standard- or user-defined and
 - either non-hierarchical (e.g., indicating the type of a variable-node) or hierarchical (e.g., indicating a parent-child relationship).
@@ -83,8 +84,8 @@ Reference types can be
 OPC UA, a protocol
 ------------------
 
-The OPC UA protocol (both binary and XML-based) is based on 25 *built-in* datatypes. In open62541, these
-are defined in ua_types.h.
+The OPC UA protocol (both binary and XML-based) is based on 25 <em>built-in</em> datatypes. In
+open62541, these are defined in ua_types.h.
 
 <table>
 <tr> <td>Boolean</td> <td>Float</td> <td>StatusCode</td> </tr>
@@ -100,7 +101,7 @@ are defined in ua_types.h.
 
 The builtin datatypes are combined to more complex structures. When the structure contains an array,
 then the size of the array is stored in an Int32 value just before the array itself. A size of -1
-indicates an undefined array. Positive size (and zero) have the usual semantics.
+indicates an undefined array. Positive sizes (and zero) have the usual semantics.
 
 Most importantly, every service has a request and a response message defined as such a data
 structure. Their exact definitions can be looked up here: