Document the lease-time, host-decl-name and pick-first-value functions.

common/dhcp-eval.5

@@ -246,7 +246,6 @@ expression.   If both expressions evaluate to null, then the result is
 null.
 .RE
 .PP
-.PP
 .B reverse (\fInumeric-expr1\fB, \fIdata-expr2\fB)\fR
 .RS 0.25i
 The two expressions are evaluated, and then the result of evaluating
@@ -295,7 +294,23 @@ Numeric-expr is evaluated and encoded as a data string of the
 specified width, in network byte order (most significant byte first).
 If the numeric expression evaluates to the null value, the result is
 also null.
-
+.PP
+.B pick-first-value (\fIdata-expr1\fR [ ... \fIexpr\fRn ] \fB)\fR
+.RS 0.25i
+The pick-first-value function takes any number of data expressions as
+its arguments.   Each expression is evaluated, starting with the first
+in the list, until an expression is found that does not evaluate to a
+null value.   That expression is returned, and none of the subsequent
+expressions are evaluated.   If all expressions evaluate to a null
+value, the null value is returned.
+.RE
+.PP
+.B host-decl-name
+.RS 0.25i
+The host-decl-name function returns the name of the host declaration
+that matched the client whose request is currently being processed, if
+any.   If no host declaration matched, the result is the null value.
+.RE
 .SH NUMERIC EXPRESSIONS
 Numeric expressions are expressions that evaluate to an integer.   In
 general, the maximum size of such an integer should not be assumed to
@@ -313,6 +328,13 @@ evaluation of the data expression doesn't provide sufficient bits to
 extract an integer of the specified size, the null value is returned.
 .RE
 .PP
+.B lease-time
+.PP
+.RS 0.25i
+The duration of the current lease - that is, the difference between
+the current time and the time that the lease expires.
+.RE
+.PP
 .I number
 .PP
 .RS 0.25i