docs: userguide: labels-custom-metadsata.md: update syntax for emtpy value labels
@@ -156,20 +156,23 @@ A Dockerfile is similar to a Makefile.
the image.
**LABEL**
- -- `LABEL <key>[=<value>] [<key>[=<value>] ...]`or
+ -- `LABEL <key>=<value> [<key>=<value> ...]`or
```
LABEL <key>[ <value>]
LABEL <key>[ <value>]
...
```
The **LABEL** instruction adds metadata to an image. A **LABEL** is a
- key-value pair. To include spaces within a **LABEL** value, use quotes and
+ key-value pair. To specify a **LABEL** without a value, simply use an empty
+ string. To include spaces within a **LABEL** value, use quotes and
backslashes as you would in command-line parsing.
```
LABEL com.example.vendor="ACME Incorporated"
- or
LABEL com.example.vendor "ACME Incorporated"
+ LABEL com.example.vendor.is-beta ""
+ LABEL com.example.vendor.is-beta=
+ LABEL com.example.vendor.is-beta=""
```
An image can have more than one label. To specify multiple labels, separate
