s4_trim(string)

Removes leading and trailing whitespace from string:

⇐ {s4_trim([
⇐     String
⇐     ])}

⇒ {String}

Inner whitespace remains intact:

⇐ {s4_trim([S  t  r
⇐     ing])}

⇒ {S  t  r
⇒     ing}

Result is quoted:

⇐ {s4_trim([m4_toupper([String])])}

⇒ {m4_toupper([String])}

(Note: m4_toupper macro is not expanded.)