Require tags to have at least one string

fixes #1193

01.md

@@ -56,7 +56,7 @@ To prevent implementation differences from creating a different event ID for the
 
 ### Tags
 
-Each tag is an array of strings of arbitrary size, with some conventions around them. Take a look at the example below:
+Each tag is an array of one or more strings, with some conventions around them. Take a look at the example below:
 
 ```jsonc
 {