pwg: improve allocation docs

diff --git a/docs/pwg/advanced-allocation.xml b/docs/pwg/advanced-allocation.xml
index 625e76e..aedf10a 100644 (file)
--- a/docs/pwg/advanced-allocation.xml
+++ b/docs/pwg/advanced-allocation.xml
@@ -41,12 +41,22 @@
       never be changed after the object is created, however, the offset
       and size can be changed.
     </para>
-    <para>
-      <classname>GstMemory</classname> objects are created by a
-      <classname>GstAllocator</classname> object. To implement support
-      for a new kind of memory type, you must implement a new allocator
-      object.
-    </para>
+    <sect2 id="section-allocation-allocator" xreflabel="GstAllocator">
+      <title>GstAllocator</title>
+      <para>
+        <classname>GstMemory</classname> objects are created by a
+        <classname>GstAllocator</classname> object. Most allocators implement the
+        default <function>gst_allocator_alloc()</function> method but some allocator
+        might implement a different method, for example when additional parameters
+        are needed to allocate the specific memory.
+      </para>
+      <para>
+        Different allocators exist for, for example, system memory, shared memory
+        and memory backed by a DMAbuf file descriptor. To implement support for a
+        new kind of memory type, you must implement a new allocator object as shown
+        below.
+      </para>
+    </sect2>
     <sect2 id="section-allocation-memory-ex" xreflabel="GstMemory-ex">
       <title>GstMemory API example</title>
       <para>
@@ -88,7 +98,7 @@
       </programlisting>
     </sect2>
 
-    <sect2 id="section-allocation-allocator" xreflabel="GstAllocator">
+    <sect2 id="section-allocation-allocator-ex" xreflabel="GstAllocator-ex">
       <title>Implementing a GstAllocator</title>
       <para>
         WRITEME
@@ -209,15 +219,10 @@
     <title>GstMeta</title>
     <para>
       With the <classname>GstMeta</classname> system you can add arbitrary
-      structures of on buffers. These structures describe extra properties
+      structures on buffers. These structures describe extra properties
       of the buffer such as cropping, stride, region of interest etc.
     </para>
     <para>
-      Metadata is also used to store, for example, the X image that is
-      backing up the memory of the buffer. This makes it easier for elements
-      to locate the X image from the buffer.
-    </para>
-    <para>
       The metadata system separates API specification (what the metadata
       and its API look like) and the implementation (how it works). This makes
       it possible to make different implementations of the same API,