m4: unclosed quote:
   quotes.m4 at line 55
1: normal
quoted string
[quoted STRING]
normal STRING
half quoted string
going up to that string

2: kill quotes
`quoted STRING'
[quoted STRING]
normal STRING
`half quoted STRING
going up to that STRING'

3: normal changed quote
`quoted STRING'
quoted string
normal STRING
`half quoted STRING
going up to that STRING'

4: empty quotes, kill them too
`quoted STRING'
[quoted STRING]
normal STRING
`half quoted STRING
going up to that STRING'

5: start quote only
quoted string'[quoted STRING]
normal STRING
half quoted stringgoing up to that STRING'

6: normal quotes are back

quoted string
[quoted STRING]
normal STRING
half quoted string
going up to that string

7: start quote+empty end quote
`quoted STRING'
quoted string]
normal string
`half quoted string
going up to that string'