1 files changed, 15 insertions, 6 deletions
diff --git a/roff.7 b/roff.7
index 6c5b6cb1..c6bb631e 100644
--- a/roff.7
+++ b/roff.7
@@ -1172,10 +1172,15 @@ Digit width space character.
 Anchor definition; ignored by
 .Xr mandoc 1 .
 .Ss \eB\(aq Ns Ar string Ns \(aq
-Test whether
+Interpolate
+.Sq 1
+if
 .Ar string
-is a numerical expession; ignored by
-.Xr mandoc 1 .
+conforms to the syntax of
+.Sx Numerical expressions
+explained above and
+.Sq 0
+otherwise.
 .Ss \eb\(aq Ns Ar string Ns \(aq
 Bracket building function; ignored by
 .Xr mandoc 1 .
@@ -1299,9 +1304,13 @@ Vertical motion; ignored by
 .Xr mandoc 1 .
 .Ss \ew\(aq Ns Ar string Ns \(aq
 Interpolate the width of the
-.Ar string ;
-ignored by
-.Xr mandoc 1 .
+.Ar string .
+The
+.Xr mandoc 1
+implementation assumes that after expansion of user-defined strings, the
+.Ar string
+only contains normal characters, no escape sequences, and that each
+character has a width of 24 basic units.
 .Ss \eX\(aq Ns Ar string Ns \(aq
 Output
 .Ar string