diff --git a/docs/dcc-validations.md b/docs/dcc-validations.md
index 10861ce..4cd0043 100644
--- a/docs/dcc-validations.md
+++ b/docs/dcc-validations.md
@@ -32,7 +32,25 @@ Check back frequently as we plan to keep growing this list of checks.
 |MINVAL|1|Defines a minimum value for a numeric cell|
 |MAXVAL|1000000|Defines a maximum value for a numeric cell|
 |HARDSELECT|sashelp.class.name|A distinct list of values (max 1000) are taken from this library.member.column reference, and the value **must** be in this list.  This list may be supplemented by entries in the MPE_SELECTBOX table.|
-|SOFTSELECT|dcdemo.mpe_tables.libref|A distinct list of values (max 1000) are taken from this library.member.column reference, and the value **may** be in this list.  This list may be supplemented by entries in the MPE_SELECTBOX table.|
-|[HARDSELECT_HOOK](/dynamic-cell-dropdown)|/logical/folder/stpname|A SAS service (STP or Viya Job) or a path to a SAS program on the filesystem.  User provided values **must** be in this list.|
-|[SOFTSELECT_HOOK](/dynamic-cell-dropdown)|/physical/path/program.sas|A SAS service (STP or Viya Job) or a path to a SAS program on the filesystem.  User provided values **may** be in this list.|
+|SOFTSELECT|dcdemo.mpe_tables.libref|A distinct list of values (max 1000) are taken from this library.member.column reference, and the user-provided value may (or may not) be in this list.  This list may be supplemented by entries in the MPE_SELECTBOX table.|
+|[HARDSELECT_HOOK](/dynamic-cell-dropdown)|/logical/folder/stpname|A SAS service (STP or Viya Job) or a path to a SAS program on the filesystem.  User provided values **must** be in this list.  Cannot be used alongside a SOFTSELECT_HOOK.|
+|[SOFTSELECT_HOOK](/dynamic-cell-dropdown)|/physical/path/program.sas|A SAS service (STP or Viya Job) or a path to a SAS program on the filesystem.  User-provided values may (or may not) be in this list.  Cannot be used alongside a HARDSELECT_HOOK.|
 
+
+## Dropdowns
+
+There are now actually FIVE places where you can configure dropdowns!
+
+1.  The MPE_SELECTBOX table
+2.  The HARDSELECT validation (library.member.column reference)
+3.  The SOFTSELECT validation (library.member.column reference)
+4.  The HARDSELECT_HOOK validation (SAS Program)
+5.  The SOFTSELECT_HOOK validation (SAS Program)
+
+How do these inter-operate?
+
+Well - if you have values in MPE_SELECTBOX and/or HARDSELECT / SOFTSELECT tables, they will be merged together, and served in ADDITION to the values provided by any HOOK program.
+
+Dropdowns are SOFT by default, unless a HARD rule is present.
+
+Data Controller will not let you submit both a HARDSELECT_HOOK and a SOFTSELECT_HOOK on the same variable.
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