Update 661-language-use.markdown

Author: Joe7M

_build/reference/661-language-use.markdown

@@ -1,7 +1,22 @@
 # USE
 
-> USE
+> USE expr
 
-Used with various commands for passing a user-defined expression. eg `SPLIT s," ",v USE TRIM(x)`. Trim each element of v.
+Used with various commands for passing a user-defined expression `expr`.
 
+### Example: Split
 
+```
+s = "/etc/temp/filename1.ext  "        ' additional spaces at the end of the string
+SPLIT s, "/", v, "temp" USE TRIM(x)    ' trim(x) will remove spaces at the beginning
+                                       ' and the end of the splitted strings;
+                                       ' try the example without "USE TRIM(x)"
+FOR i = 0 TO UBOUND(v)
+  PRINT i;" [";v(i);"]"
+NEXT
+
+' displays
+' 0 []
+' 1 [etc/temp]
+' 2 [filename1.ext]
+```