diff --git a/doc/manual.adoc b/doc/manual.adoc
index 1e84a92..34744c0 100644
--- a/doc/manual.adoc
+++ b/doc/manual.adoc
@@ -71,6 +71,20 @@ A table definition directive consists of a record containing the values `def`
 and the table name.  A table must be defined before any field definitions can
 occur for that table.
 
+==== Field Definition Directives (`fld` and `dsc`)
+
+Field definitions come in two types.  The first, `fld`, provides a mapping for
+imported data, and `dsc` does not.  They are otherwise identical.
+
+A field definition directive consists of a record containing the values `fld` or
+`dsc`, the name of the table, the field number for imported data (or empty for
+`dsc`), the field number for use in newfol, an optional Python 3 expression, and
+a description.
+
+The Python 3 expression is evaluated and placed in the field when creating a new
+record.  This can be used, for example, to automatically insert the date into a
+particular field.
+
 === Configuration File
 
 Configuration files are identical to schema files except that instead of the