diff --git a/src/build/virtual-target.jam b/src/build/virtual-target.jam
index 95e88e80c..eff94a9c9 100644
--- a/src/build/virtual-target.jam
+++ b/src/build/virtual-target.jam
@@ -18,31 +18,46 @@ import type ;
 #                       +--------------------------+
 #                       | actualize-action() = 0   |
 #                       | actualize-location() = 0 |
-#                       +------------+-------------+
-#                                    |
-#                                    ^
-#                                   / \
-#                                  +-+-+
-#                                    |
-#    +-------------+       +---------+------------+
-#    | action      |       | abstract-file-target |
-#    +=============+       +======================+
-#    | action-name |   +---+ action               |
-#    +-------------+   |   | actualize-action()   |
-#    | actualize() +---+   +---------+------------+
-#    | path()      |                 |
-#    +------+------+                 ^
-#           |                       / \
-#           ^                      +-+-+
-#          / \                       |
-#         +-+-+              +-------+-------------------+
-#           |                |                           |
-#    +------+------+  +------+---------------+  +--------+-------------+
-#    | link-action |  | file-target          |  | searched-lib-target  |
-#    +=============+  +======================+  +======================+
-#    |             |  | actualize-location() |  | actualize-location() |
-#    +-------------+  +----------------------+  +----------------------+
+#                       +----------------+---------+
+#                                        |
+#                                        ^
+#                                       / \
+#                                      +-+-+
+#                                        |
+#    +---------------------+     +---------+------------+
+#    | action              |     | abstract-file-target |
+#    +=====================|   1 +======================+
+#    | action-name         |  +--| action               |
+#    | properties          |  |  +----------------------+
+#    +---------------------+--+  | actualize-action()   |
+#    | actualize()         |0..1 +-----------+----------+
+#    | path()              |                 |
+#    | adjust-properties() |                 |
+#    | actualize-sources() |                 |
+#    +------+--------------+                 ^
+#           |                               / \
+#           ^                              +-+-+
+#          / \                               |
+#         +-+-+                +-------------|-------------+
+#           |                  |                           |
+#           |           +------+---------------+  +--------+-------------+
+#           |           | file-target          |  | searched-lib-target  |
+#           |           +======================+  +======================+
+#           |           | actualize-location() |  | actualize-location() |
+#           |           +----------------------+  +----------------------+
+#           |
+#         +--------------------------------+
+#         |                                |
+#    +---------------------+     +---------------------+
+#    | compile-action      |     | link-action         |
+#    +=====================+     +=====================+
+#    | adjust-properties() |     | adjust-properties() |
+#    +---------------------+     | actualize-sources() |
+#                                +---------------------+
 #
+# The 'compile-action' and 'link-action' classes are defined not here,
+# but in builtin.jam modules. They are shown in the diagram to give
+# the big picture.
 
 # Potential target. It can be converted into jam target and used in
 # building, if needed. However, it can be also dropped, which allows
diff --git a/src/tools/builtin.jam b/src/tools/builtin.jam
index ef932d220..9a2a4fc7d 100644
--- a/src/tools/builtin.jam
+++ b/src/tools/builtin.jam
@@ -358,6 +358,9 @@ rule compile-action ( targets + : sources * : action-name : properties * )
 {
     action.__init__ $(targets) : $(sources) : $(action-name) : $(properties) ;
     
+    # For all virtual targets for the same dependency graph as self, 
+    # i.e. which belong to the same main target, add their directories
+    # to include path.
     rule adjust-properties ( properties * )
     {
         local dg = [ $(self.targets[1]).dg ] ;
@@ -402,6 +405,11 @@ rule link-action ( targets + : sources * : action-name : properties * )
 {
     action.__init__ $(targets) : $(sources) : $(action-name) : $(properties) ;
 
+    # For all sources which are instances searched-lib-targets, add
+    # appropriate <find-shared-library> or <find-static-library> propertry
+    # For all library sources, add <library> property with that source.
+    # If <hardcode-dll-paths>true is in properties, for each library source
+    # add <dll-path> property with the absolute path to that library.
     rule adjust-properties ( properties * )
     {        
         local hardcore-rpath ;
@@ -454,7 +462,9 @@ rule link-action ( targets + : sources * : action-name : properties * )
         return $(properties) ;        
     }
     
-    
+    # Filters out all sources which are of LIB type and actualizes the remaining
+    # sources by calling base method.
+    # Library sources are handled by "adjust-properties" above.
     rule actualize-sources ( sources * )
     {
         local real-sources ;