updated docs based on review

Author: Jolanrensen

core/generated-sources/src/main/kotlin/org/jetbrains/kotlinx/dataframe/documentation/UnifyingNumbers.kt

@@ -27,7 +27,7 @@ import org.jetbrains.kotlinx.dataframe.impl.UnifiedNumberTypeOptions
  *    UByte     Byte
  *        \     /
  *        \    /
- *       Nothing?
+ *       Nothing
  * ```
  * For each number type in the graph, it holds that a number of that type can be expressed lossless by
  * a number of a more complex type (any of its parents).
@@ -40,7 +40,11 @@ import org.jetbrains.kotlinx.dataframe.impl.UnifiedNumberTypeOptions
  *
  * See [UnifiedNumberTypeOptions] for these settings.
  *
- * At the bottom of the graph is [Nothing?][Nothing].
- * This can be interpreted as `null`.
+ * Nullability, while not displayed in the graph, is also taken into account.
+ * This means that `Int?` and `Float` will be unified to `Double?`.
+ *
+ * At the bottom of the graph is [Nothing].
+ * This can be interpreted as "no type" and can have no instance,
+ * while [Nothing?][Nothing] can only be `null`.
  */
 public interface UnifyingNumbers

core/generated-sources/src/main/kotlin/org/jetbrains/kotlinx/dataframe/impl/NumberTypeUtils.kt

@@ -52,7 +52,7 @@ private val unifiedNumberTypeGraphs = mutableMapOf<UnifiedNumberTypeOptions, Dir
  *    UByte     Byte
  *        \     /
  *        \    /
- *       Nothing?
+ *       Nothing
  * ```
  *
  * For any two numbers, we can find the nearest common ancestor in this graph
@@ -127,7 +127,7 @@ internal fun getUnifiedNumberTypeGraph(
  *    UByte     Byte
  *        \     /
  *        \    /
- *       Nothing?
+ *       Nothing
  * ```
  *
  * For any two numbers, we can find the nearest common ancestor in this graph

core/generated-sources/src/test/kotlin/org/jetbrains/kotlinx/dataframe/types/UtilTests.kt

@@ -438,7 +438,7 @@ class UtilTests {
      *    UByte     Byte
      *        \     /
      *        \    /
-     *       Nothing?
+     *       Nothing
      * ```
      */
     @Test

core/src/main/kotlin/org/jetbrains/kotlinx/dataframe/documentation/UnifyingNumbers.kt

@@ -22,8 +22,12 @@ import org.jetbrains.kotlinx.dataframe.impl.UnifiedNumberTypeOptions
  *
  * See [UnifiedNumberTypeOptions] for these settings.
  *
- * At the bottom of the graph is [Nothing?][Nothing].
- * This can be interpreted as `null`.
+ * Nullability, while not displayed in the graph, is also taken into account.
+ * This means that `Int?` and `Float` will be unified to `Double?`.
+ *
+ * At the bottom of the graph is [Nothing].
+ * This can be interpreted as "no type" and can have no instance,
+ * while [Nothing?][Nothing] can only be `null`.
  */
 public interface UnifyingNumbers {
 
@@ -45,7 +49,7 @@ public interface UnifyingNumbers {
      *    UByte     Byte
      *        \\     /
      *        \\    /
-     *       Nothing?
+     *       Nothing
      * ```
      */
     @ExcludeFromSources

docs/StardustDocs/resources/snippets/kdocs/org.jetbrains.kotlinx.dataframe.documentation.UnifyingNumbers.Graph.html

@@ -101,6 +101,6 @@
    UByte     Byte
        \     /
        \    /
-      Nothing?
+      Nothing
 </code></pre></body>
 <html/>

docs/StardustDocs/topics/numberUnification.md

@@ -1,8 +1,9 @@
 [//]: # (title: Number Unification)
 
-The concept of unifying numbers is converting them to a common number type without losing information.
+Unifying numbers means converting them to a common number type without losing information.
 
-This is an internal part of the library for now, but its logic can be encountered in multiple places, such as
+This is currently an internal part of the library, 
+but its logic implementation can be encountered in multiple places, such as
 [statistics](summaryStatistics.md), and [reading JSON](read.md#read-from-json). 
 
 The following graph shows the hierarchy of number types in Kotlin DataFrame.
@@ -15,10 +16,11 @@ For each number type in the graph, it holds that a number of that type can be ex
 a number of a more complex type (any of its parents).
 This is either because the more complex type has a larger range or higher precision (in terms of bits).
 
-Nullability, while not displayed everywhere in the graph, is also taken into account.
+Nullability, while not displayed in the graph, is also taken into account.
 This means that `Int?` and `Float` will be unified to `Double?`.
 
-At the bottom of the graph is `Nothing?`. This can be interpreted as `null`.
+`Nothing` is at the bottom of the graph and is the starting point in unification.
+This can be interpreted as "no type" and can have no instance, while `Nothing?` can only be `null`.
 
 > There may be parts of the library that "unify" numbers, such as [`readCsv`](read.md#column-type-inference-from-csv),
 > or [`readExcel`](read.md#read-from-excel).