diff --git a/test/didchange.xq b/test/didchange.xq
index b18fe38..e0a3c66 100644
--- a/test/didchange.xq
+++ b/test/didchange.xq
@@ -1 +1,14 @@
-json:doc("sample.msg/didChange/client2.json",{"format":"w3"})
+import module namespace pos="lsp/position" at "../webapp/lsp/position.xqm";
+
+declare variable $msg:=json:doc("sample.msg/didChange/client2.json",{"format":"w3"});
+declare variable $text:=`12345678
+bbbbb
+cccccc`;
+
+
+
+
+
+(: return pos:resolvePosition($text,$p) :)
+ pos:apply-changes($text,$msg?params?contentChanges)
+(: $msg?params?contentChanges :) 
\ No newline at end of file
diff --git a/webapp/lsp/docs.xqm b/webapp/lsp/docs.xqm
index e0a59b1..a36fd45 100644
--- a/webapp/lsp/docs.xqm
+++ b/webapp/lsp/docs.xqm
@@ -5,15 +5,8 @@
 :)
 module namespace docs="lsp/docs";
 import module namespace p="xq4" at "xq4.xqm";
+import module namespace pos="lsp/position" at "position.xqm";
 
-(:~ 
-@param line Line position in a document (zero-based).
-@param character Character offset on a line in a document (zero-based).
-:)
-declare record docs:Position(
-	line as xs:integer,
-	character as xs:integer
-);
 
 (: document info :)
 declare type docs:property as enum(
@@ -58,29 +51,3 @@ return (
 ) 
 };
 
-declare function docs:resolvePosition($text as xs:string, $pos as docs:Position) 
-as xs:integer
-{
-  (: let line = 0, off = 0
-  while (line < pos.line) {
-    let next = text.indexOf("\n", off)
-    if (!next) throw new RangeError("Position out of bounds")
-    off = next + 1
-    line++
-  }
-  off += pos.character
-  if (off > string-length($text)) throw new RangeError("Position out of bounds")
-  return off :)
-  0
-};
-
-declare function docs:toPosition($text as xs:string, $pos as xs:integer)
-as docs:Position {
-  (: for (let off = 0, line = 0;;) {
-    let next = text.indexOf("\n", off)
-    if (next < 0 || next >= pos) return {line, character: pos - off}
-    off = next + 1
-    line++
-  } :)
-  docs:Position(0,0)
-};
\ No newline at end of file
diff --git a/webapp/lsp/parse.xq b/webapp/lsp/parse.xq
index eeae300..9dc8ce4 100644
--- a/webapp/lsp/parse.xq
+++ b/webapp/lsp/parse.xq
@@ -5,10 +5,10 @@ import module namespace docs="lsp/docs" at "docs.xqm";
 declare variable $params  as map(*) external;
 declare variable $webSocket as xs:string external;
 
-prof:time(docs:save(
+docs:save(
     $webSocket,
     $params 
-),"⏱️ doc:save "),
+)=>prof:time("⏱️ doc:save "),
 
 ws:send(
     {"jsonrpc": "2.0",
diff --git a/webapp/lsp/position.xqm b/webapp/lsp/position.xqm
new file mode 100644
index 0000000..47d0eb5
--- /dev/null
+++ b/webapp/lsp/position.xqm
@@ -0,0 +1,67 @@
+(:~
+text editing API
+:)
+module namespace pos="lsp/position";
+
+(:~ 
+@param line Line position in a document (zero-based).
+@param character Character offset on a line in a document (zero-based).
+:)
+declare record pos:Position(
+	line as xs:integer,
+	character as xs:integer
+);
+
+declare function pos:apply-changes($text as xs:string, $chs as array(*))
+as xs:string{
+array:fold-left($chs,$text,pos:apply-change#2)
+}; 
+
+(:~ text updated with $ch changes from didChange :)
+declare function pos:apply-change($text as xs:string, $ch as map(*))
+as xs:string{
+ if(exists($ch?range))
+ then substring($text,1, pos:resolvePosition($text, $ch?range?start)) 
+      || $ch?text ||
+      substring($text,pos:resolvePosition($text, $ch?range?end))
+ else $ch?text 
+}; 
+
+(:~ find index from Position :)
+declare function pos:resolvePosition($text as xs:string, $pos as map(*)) 
+as xs:integer
+{
+  let $nl:=characters($text)=>index-of(char("\n"))
+  let $s:=  while-do(
+  map{"off":0,"line":0}, 
+  fn($r, $i){$r?line < $pos?line},
+  fn($r,$i){ let $next:=$nl[$i] 
+             return if(empty($next))
+                    then error(xs:QName("docs:range"),"bad line")
+                    else {"off": $next+1,"line":$r?line+1}=>trace("AA ") }
+)
+  let $off:= $s?off+$pos?character
+  return if($off>string-length($text))
+        then error(xs:QName("docs:range"),"bad offset")
+        else xs:integer($off)
+  
+};
+
+(:~  convert index into Position :)
+declare function pos:toPosition($text as xs:string, $pos as xs:integer)
+as pos:Position {
+  let $nl:=characters($text)=>index-of(char("\n"))
+  let $predicate:=fn($r, $i){
+      let $next:=$nl[$i=>trace("I ")] 
+      return exists($next) and $next < $pos
+}
+        
+  let $s:=  while-do(
+  map{"off":0,"line":0}, 
+  $predicate,
+  fn($r,$i){ let $next:=$nl[$i] return {"off": $next+1,"line":$r?line+1}=>trace("AA ") }
+)
+return pos:Position($s?line,  $pos - $s?off)            
+};
+ 
+