diff --git a/service2.js b/service2.js
index a3ef4bb..425c941 100644
--- a/service2.js
+++ b/service2.js
@@ -161,8 +161,7 @@ class BesService {
     const clientRects = range.getClientRects()
     const scrollPanelRect = this.scrollPanel.getBoundingClientRect()
     let highlights = []
-    for (let i = 0, n = clientRects.length; i < n; ++i) {
-      const rect = clientRects[i]
+    for (let rect of clientRects) {
       const highlight = document.createElement('div')
       highlight.classList.add('bes-typo-mistake')
       highlight.style.left = `${rect.left - scrollPanelRect.left}px`
@@ -251,6 +250,41 @@ class BesService {
     this.scrollPanel.style.height = `${this.hostElement.scrollHeight}px`
   }
 
+  /**
+   * Displays correction panel.
+   *
+   * @param {*} el Block element/paragraph containing grammar checking rule match
+   * @param {*} match Grammar checking rule match
+   * @param {PointerEvent} source Click event source
+   */
+  popupCorrectionPanel(el, match, source) {
+    const popup = document.querySelector('bes-popup-el')
+    popup.changeMessage(match.match.message)
+    popup.appendReplacements(
+      el,
+      match,
+      this,
+      this.hostElement.contentEditable !== 'false'
+    )
+    popup.show(source.clientX, source.clientY)
+  }
+
+  /**
+   * Replaces grammar checking match with a suggestion provided by grammar checking service.
+   *
+   * @param {*} el Block element/paragraph containing grammar checking rule match
+   * @param {*} match Grammar checking rule match
+   * @param {String} replacement Text to replace grammar checking match with
+   */
+  replaceText(el, match, replacement) {
+    if (this.timer) clearTimeout(this.timer)
+    if (this.abortController) this.abortController.abort()
+    this.clearProofing(el)
+    match.range.deleteContents()
+    match.range.insertNode(document.createTextNode(replacement))
+    this.proofAll()
+  }
+
   /**
    * Repositions status DIV element.
    */
@@ -282,12 +316,30 @@ class BesService {
   }
 }
 
+/*************************************************************************
+ *
+ * Grammar-checking service base class for tree-organized editors
+ *
+ *************************************************************************/
+class BesTreeService extends BesService {
+  constructor(hostElement) {
+    super(hostElement)
+  }
+
+  /**
+   * Unregisters grammar checking service.
+   */
+  unregister() {
+    super.unregister()
+  }
+}
+
 /*************************************************************************
  *
  * DOM grammar-checking service
  *
  *************************************************************************/
-class BesDOMService extends BesService {
+class BesDOMService extends BesTreeService {
   constructor(hostElement) {
     super(hostElement)
     this.onBeforeInput = this.onBeforeInput.bind(this)
@@ -492,7 +544,7 @@ class BesDOMService extends BesService {
    * Tests if given block element has already been grammar-checked.
    *
    * @param {Element} el DOM element to check
-   * @returns {*} Result of grammar check if the element has already been grammar-checked; null otherwise.
+   * @returns {*} Result of grammar check if the element has already been grammar-checked; undefined otherwise.
    */
   getProofing(el) {
     return this.results.find(result =>
@@ -688,47 +740,21 @@ class BesDOMService extends BesService {
     const el = this.getBlockParent(source.targetElement || source.target)
     if (!el) return
 
-    const matches = this.results.find(child =>
+    const result = this.results.find(child =>
       BesDOMService.isSameParagraph(child.element, el)
-    )?.matches
-    if (matches) {
-      for (let m of matches) {
-        if (m.rects) {
-          for (let r of m.rects) {
-            if (BesService.isPointInRect(source.clientX, source.clientY, r)) {
-              const popup = document.querySelector('bes-popup-el')
-              popup.changeMessage(m.match.message)
-              popup.appendReplacements(
-                el,
-                m,
-                this,
-                this.hostElement.contentEditable !== 'false'
-              )
-              popup.show(source.clientX, source.clientY)
-              return
-            }
+    )
+    if (result) {
+      for (let m of result.matches) {
+        for (let r of m.rects) {
+          if (BesService.isPointInRect(source.clientX, source.clientY, r)) {
+            this.popupCorrectionPanel(el, m, source)
+            return
           }
         }
       }
     }
     BesPopup.hide()
   }
-
-  /**
-   * Replaces grammar checking match with a suggestion provided by grammar checking service.
-   *
-   * @param {Element} el Block element containing grammar checking rule match
-   * @param {*} match Grammar checking rule match
-   * @param {String} replacement Text to replace grammar checking match with
-   */
-  replaceText(el, match, replacement) {
-    if (this.timer) clearTimeout(this.timer)
-    if (this.abortController) this.abortController.abort()
-    this.clearProofing(el)
-    match.range.deleteContents()
-    match.range.insertNode(document.createTextNode(replacement))
-    this.proofAll()
-  }
 }
 
 /*************************************************************************
@@ -1021,7 +1047,7 @@ class BesPlainTextService extends BesService {
    * Tests if given paragraph has already been grammar-checked.
    *
    * @param {Range} range Paragraph range
-   * @returns {*} Result of grammar check if the element has already been grammar-checked; null otherwise.
+   * @returns {*} Result of grammar check if the element has already been grammar-checked; undefined otherwise.
    */
   getProofing(range) {
     return this.results.find(result =>
@@ -1128,45 +1154,17 @@ class BesPlainTextService extends BesService {
     if (!el) return
 
     for (let result of this.results) {
-      if (result.matches) {
-        for (let m of result.matches) {
-          if (m.rects) {
-            for (let r of m.rects) {
-              if (BesService.isPointInRect(source.clientX, source.clientY, r)) {
-                const popup = document.querySelector('bes-popup-el')
-                popup.changeMessage(m.match.message)
-                popup.appendReplacements(
-                  result.range,
-                  m,
-                  this,
-                  this.hostElement.contentEditable !== 'false'
-                )
-                popup.show(source.clientX, source.clientY)
-                return
-              }
-            }
+      for (let m of result.matches) {
+        for (let r of m.rects) {
+          if (BesService.isPointInRect(source.clientX, source.clientY, r)) {
+            this.popupCorrectionPanel(result.range, m, source)
+            return
           }
         }
       }
     }
     BesPopup.hide()
   }
-
-  /**
-   * Replaces grammar checking match with a suggestion provided by grammar checking service.
-   *
-   * @param {Range} range Paragraph range
-   * @param {*} match Grammar checking rule match
-   * @param {String} replacement Text to replace grammar checking match with
-   */
-  replaceText(range, match, replacement) {
-    if (this.timer) clearTimeout(this.timer)
-    if (this.abortController) this.abortController.abort()
-    this.clearProofing(range)
-    match.range.deleteContents()
-    match.range.insertNode(document.createTextNode(replacement))
-    this.proofAll()
-  }
 }
 
 /*************************************************************************