diff --git a/bash.md b/bash.md
index 001186ee6..e9bb11ff8 100644
--- a/bash.md
+++ b/bash.md
@@ -211,15 +211,16 @@ echo ${STR^}   #=> "Hello world!" (uppercase 1st letter)
 echo ${STR^^}  #=> "HELLO WORLD!" (all uppercase)
 ```
 
-
 ### Default values
 
-| `${FOO:-val}`        | `$FOO`, or `val` if not set |
-| `${FOO:=val}`        | Set `$FOO` to `val` if not set |
-| `${FOO:+val}`        | `val` if `$FOO` is set |
-| `${FOO:?message}`    | Show error message and exit if `$FOO` is not set |
+| Expression        | Description                                              |
+| ----------------- | -------------------------------------------------------- |
+| `${FOO:-val}`     | `$FOO`, or `val` if unset (or null)                      |
+| `${FOO:=val}`     | Set `$FOO` to `val` if unset (or null)                   |
+| `${FOO:+val}`     | `val` if `$FOO` is set (and not null)                    |
+| `${FOO:?message}` | Show error message and exit if `$FOO` is unset (or null) |
 
-The `:` is optional (eg, `${FOO=word}` works)
+Omitting the `:` removes the (non)nullity checks, e.g. `${FOO-val}` expands to `val` if unset otherwise `$FOO`.
 
 Loops
 -----