Difference between GStreamer 0.10 Library Reference Manual and GStreamer 0.10 Core Reference Manual

I am just going through the gstreamer documentation.I couldnt understand the difference between the GStreamer 0.10 Library Reference Manual and GStreamer 0.10 Core Reference Manual.Most of the fuinction calls like gst_X_funtion_name cab be interpreted from the GStreamer 0.10 Core Reference by checking the Gst_X documentation.But why GStreamer 0.10 Library Reference Manual is used and where it is used.
Plz elaborate.
Rgds
Softy

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