Introduce ResolvedPos.textOffset, deprecate atNodeBoundary

FEATURE: Resolved positions have a new getter
[`textOffset`](##model.ResolvedPos.textOffset) to find their position
within a text node (if any).

BREAKING: `ResolvedPos.atNodeBoundary` is deprecated and will be
removed in the next release. Use `textOffset > 0` instead.

src/node.js

@@ -230,7 +230,7 @@ class Node {
     // In an empty parent, return the empty array
     if (parent.content.size == 0) return Mark.none
     // When inside a text node or at the start of the parent node, return the node's marks
-    if (useAfter || index == 0 || !$pos.atNodeBoundary) return parent.child(index).marks
+    if (useAfter || index == 0 || $pos.textOffset) return parent.child(index).marks
 
     let marks = parent.child(index - 1).marks
     for (var i = 0; i < marks.length; i++) if (marks[i].type.spec.inclusiveRight === false)

src/replace.js

@@ -151,13 +151,13 @@ function addRange($start, $end, depth, target) {
     startIndex = $start.index(depth)
     if ($start.depth > depth) {
       startIndex++
-    } else if (!$start.atNodeBoundary) {
+    } else if ($start.textOffset) {
       addNode($start.nodeAfter, target)
       startIndex++
     }
   }
   for (let i = startIndex; i < endIndex; i++) addNode(node.child(i), target)
-  if ($end && $end.depth == depth && !$end.atNodeBoundary)
+  if ($end && $end.depth == depth && $end.textOffset)
     addNode($end.nodeBefore, target)
 }
 

src/resolvedpos.js

@@ -1,3 +1,5 @@
+let warnedAboutBoundary = false
+
 // ::- You'll often have to '[resolve](#model.Node.resolve)' a
 // position to get the context you need. Objects of this class
 // represent such a resolved position, providing various pieces of
@@ -48,7 +50,7 @@ class ResolvedPos {
   // given level.
   indexAfter(depth) {
     depth = this.resolveDepth(depth)
-    return this.index(depth) + (depth == this.depth && this.atNodeBoundary ? 0 : 1)
+    return this.index(depth) + (depth == this.depth && !this.textOffset ? 0 : 1)
   }
 
   // :: (?number) → number
@@ -87,10 +89,19 @@ class ResolvedPos {
     return depth == this.depth + 1 ? this.pos : this.path[depth * 3 - 1] + this.path[depth * 3].nodeSize
   }
 
-  // :: bool
-  // True if this position points at a node boundary, false if it
-  // points into a text node.
-  get atNodeBoundary() { return this.path[this.path.length - 1] == this.pos }
+  get atNodeBoundary() {
+    if (!warnedAboutBoundary && typeof console != "undefined") {
+      warnedAboutBoundary = true
+      console.warn("ResolvedPos.atNodeBoundary is deprecated. Use textOffset > 0 instead")
+    }
+    return !this.textOffset
+  }
+
+  // :: number
+  // When this position points into a text node, this returns the
+  // distance between the position and the start of the text node.
+  // Will be zero for positions that point between nodes.
+  get textOffset() { return this.pos - this.path[this.path.length - 1] }
 
   // :: ?Node
   // Get the node directly after the position, if any. If the position