diff --git a/idea/idea-fir/src/org/jetbrains/kotlin/idea/fir/api/applicator/HLApplicabilityRange.kt b/idea/idea-fir/src/org/jetbrains/kotlin/idea/fir/api/applicator/HLApplicabilityRange.kt
index 5cb51b9376f..e0d962f0e13 100644
--- a/idea/idea-fir/src/org/jetbrains/kotlin/idea/fir/api/applicator/HLApplicabilityRange.kt
+++ b/idea/idea-fir/src/org/jetbrains/kotlin/idea/fir/api/applicator/HLApplicabilityRange.kt
@@ -10,10 +10,23 @@ import com.intellij.psi.PsiElement
 import org.jetbrains.kotlin.idea.util.textRangeIn
 import org.jetbrains.kotlin.psi.KtElement
 
+/**
+ * Provide list of ranges on which [HLApplicator] is available
+ *
+ * It should not do some additional checks to verify that  [HLApplicator] is applicable
+ * as it is responsibility of [HLApplicator.isApplicableByPsi]
+ *
+ * No resolve operations should be called inside [getApplicabilityRanges]
+ * I.e no [org.jetbrains.kotlin.idea.frontend.api.KtAnalysisSession] or [PsiElement] resolve can be used inside
+ *
+ * [getApplicabilityRanges] is guarantied to be called inside read action
+ */
 sealed class HLApplicabilityRange<in ELEMENT : PsiElement> {
     /**
-     * Returns the list of ranges on which [HLApplicator] is available
+     * Return the list of ranges on which [HLApplicator] is available
+     *
      * The ranges are relative to [element]
+     *  i.e. if range covers the whole element when it should return `[0, element.length)`
      */
     abstract fun getApplicabilityRanges(element: ELEMENT): List<TextRange>
 }
@@ -25,17 +38,60 @@ private class HLApplicabilityRangeImpl<ELEMENT : PsiElement>(
         getApplicabilityRanges.invoke(element)
 }
 
+/**
+ * Create [HLApplicabilityRange] by list of possible ranges
+ * [getRanges] should return `empty list if no applicability ranges found
 
+ * [getRanges] should return ranges relative to passed [ELEMENT]
+ * i.e. if range covers the whole element when it should return `[0, element.length)`
+ *
+ * No resolve operations should be called inside [getRanges]
+ * I.e no [KtAnalyisSession] or [PsiElement] resolve can be used inside
+ *
+ * [getRanges] is guarantied to be called inside read action
+ *
+ * @see applicabilityRange
+ * @see applicabilityTarget
+ */
 fun <ELEMENT : KtElement> applicabilityRanges(
     getRanges: (ELEMENT) -> List<TextRange>
 ): HLApplicabilityRange<ELEMENT> =
     HLApplicabilityRangeImpl(getRanges)
 
+/**
+ * Create [HLApplicabilityRange] with a single applicability range
+ * [getRange] should return `null` if no applicability ranges found
+ *
+ * No resolve operations should be called inside [getRanges]
+ * I.e no [KtAnalyisSession] or [PsiElement] resolve can be used inside
+ *
+ * [getRange] should return range relative to passed [ELEMENT]
+ * i.e. if range covers the whole element when it should return `[0, element.length)`
+ *
+ * [getRange] is guarantied to be called inside read action
+ *
+ * @see applicabilityRanges
+ * @see applicabilityTarget
+ */
 fun <ELEMENT : KtElement> applicabilityRange(
     getRange: (ELEMENT) -> TextRange?
 ): HLApplicabilityRange<ELEMENT> =
     HLApplicabilityRangeImpl { listOfNotNull(getRange(it)) }
 
+/**
+ * Create [HLApplicabilityRange] with a single applicability range represented by [PsiElement]
+ * [getTarget] should return [PsiElement] which range will be used or `null` if no applicability ranges found
+ *
+ * No resolve operations should be called inside [getTarget]
+ * I.e no [KtAnalyisSession] or [PsiElement] resolve can be used inside
+ *
+ * [getTarget] should return element inside the element passed
+ *
+ * [getTarget] is guarantied to be called inside read action
+ *
+ * @see applicabilityRanges
+ * @see applicabilityTarget
+ */
 fun <ELEMENT : PsiElement> applicabilityTarget(
     getTarget: (ELEMENT) -> PsiElement?
 ): HLApplicabilityRange<ELEMENT> =