Improve wording and spelling consistency in UPGRADING

[ci skip]

Author: theodorejb

UPGRADING

@@ -217,26 +217,24 @@ PHP 8.0 UPGRADE NOTES
   . debug_backtrace() and Exception::getTrace() will no longer provide
     references to arguments. It will not be possible to change function
     arguments through the backtrace.
-  . The concept of numeric-string has been altered to be less error prone.
-    Trailing whitespaces are now allowed in numeric strings making it symmetric
-    with how leading whitespaces were treated.
-    This mostly affects:
+  . Numeric string handling has been altered to be more intuitive and less
+    error-prone. Trailing whitespace is now allowed in numeric strings for
+    consistency with how leading whitespace is treated. This mostly affects:
      - The is_numeric() function
      - String-to-string comparisons
      - Type declarations
-     - Increment and Decrement operations
-    The concept of "leading-numeric string" has been mostly dropped, the cases
-    where this concept remains is in order to ease migration.
-    String which emitted an E_NOTICE "A non well formed numeric value encountered"
-    will now emit an E_WARNING "A non-numeric value encountered"
-    and all strings which emitted an E_WARNING "A non-numeric value encountered"
-    will now throw a TypeError.
-    This mostly affects:
+     - Increment and decrement operations
+    The concept of a "leading-numeric string" has been mostly dropped; the
+    cases where this remains exist in order to ease migration. Strings which
+    emitted an E_NOTICE "A non well formed numeric value encountered" will now
+    emit an E_WARNING "A non-numeric value encountered" and all strings which
+    emitted an E_WARNING "A non-numeric value encountered" will now throw a
+    TypeError. This mostly affects:
      - Arithmetic operations
      - Bitwise operations
     This E_WARNING to TypeError change also affects the E_WARNING
-    "Illegal string offset 'string'" for illegal string offsets.
-    This does not change the behaviour of explicit casts to int/float from strings.
+    "Illegal string offset 'string'" for illegal string offsets. The behavior
+    of explicit casts to int/float from strings has not been changed.
     RFC: https://wiki.php.net/rfc/saner-numeric-strings
 
 - COM:
@@ -356,7 +354,7 @@ PHP 8.0 UPGRADE NOTES
     now be empty.
   . The $is_hex parameter, which was not used internally, has been removed from
     mb_decode_numericentity().
-  . The legacy behaviour of passing the encoding as the third argument instead
+  . The legacy behavior of passing the encoding as the third argument instead
     of an offset for the mb_strrpos() function has been removed, provide an
     explicit 0 offset with the encoding as the fourth argument instead.
   . The ISO_8859-* character encoding aliases have been replaced by ISO8859-*
@@ -370,7 +368,7 @@ PHP 8.0 UPGRADE NOTES
 
 - PCRE:
   . When passing invalid escape sequences they are no longer interpreted as
-    literals. This behaviour previously required the X modifier - which is
+    literals. This behavior previously required the X modifier - which is
     now ignored.
 
 - PDO: