Improve doc for .struct/.union

git-svn-id: svn://svn.cc65.org/cc65/trunk@3365 b7a2c559-68d2-44c3-8de9-860c34a00d81

doc/ca65.sgml

@@ -3730,12 +3730,17 @@ compiler, depending on the target system selected:
 
 <sect>Structs and unions<label id="structs"><p>
 
+<sect1>Overview<p>
+
 Structs and unions are special forms of <ref id="scopes" name="scopes">.  They
 are to some degree comparable to their C counterparts. Both have a list of
 members. Each member allocates storage and may optionally have a name, which,
 in case of a struct, is the offset from the beginning and, in case of a union,
 is always zero.
 
+
+<sect1>Declaration<p>
+
 Here is an example for a very simple struct with two members and a total size
 of 4 bytes:
 
@@ -3765,8 +3770,11 @@ storage allocators may contain a multiplier, as in the example below:
       .endstruct
 </verb></tscreen>
 
-Using the <ref id=".TAG" name=".TAG"> keyword, it is possible to embedd
-already defined structs or unions in structs:
+
+<sect1>The <tt/.TAG/ keyword<p>
+
+Using the <ref id=".TAG" name=".TAG"> keyword, it is possible to reserve space
+for an already defined struct or unions within another struct:
 
 <tscreen><verb>
       .struct Point
@@ -3798,6 +3806,18 @@ of the struct itself:
 This may change in a future version of the assembler.
 
 
+<sect1>Limitations<p>
+
+Structs and unions are currently implemented as nested symbol tables (in fact,
+they were a by-product of the improved scoping rules). Currently, the
+assembler has no idea of types. This means that the <ref id=".TAG"
+name=".TAG"> keyword will only allocate space. You won't be able to initialize
+variables declared with <ref id=".TAG" name=".TAG">, and adding an embedded
+structure to another structure with <ref id=".TAG" name=".TAG"> will not make
+this structure accessible by using the '::' operator.
+
+
+
 <sect>Module constructors/destructors<label id="condes"><p>
 
 <em>Note:</em> This section applies mostly to C programs, so the explanation