Minor updates to documentation.

JetCore.txt

@@ -32,6 +32,26 @@ functionality for each tag.
 Outputting a database from mysql may be performed using the <mysql> tag
 in combination with the <ifrow>, <whilerow> and <sql> tags.  
 
+\section{User Defined Tags and Tag Liraries}
+
+You can define your own tag definitions and use them within your JET
+scripts. 
+
+Keywords are not defined as part of the tag definition and any
+attribute added to the implementation of the tag is passed into the
+tag process as a local variable for that container. 
+
+A <container /> tag can be inserted into the container and will take
+the contents of the container at runtime and insert it into the output
+when processing the user defined tag definition. The container tag of
+the the <container /> is processed before the container containing the
+<container /> so that local variabls can be set and processed that
+will affect the tags overall output. 
+
+Tags are many times nested with tags running within the container of a
+higher tag. 
+
+
 
 \chapter{Variables and Variable Types}