docs: clarify UTF-8 indexing explanation and fix punctuation in string and values documentation

doc/site/core/string.markdown

@@ -10,8 +10,8 @@ get involved, it's important to understand the distinction.
 
 In UTF-8, a single Unicode code point (very roughly a single "character") may
 be encoded as one or more bytes. This means you can't directly index by code
-point. There's no way to find, say, the fifth code unit in a string without
-walking the string from the beginning and counting them as you go.
+point. There's no way to jump directly to, say, the fifth code unit in a string
+without walking the string from the beginning and counting them as you go.
 
 Because counting code units is relatively slow, string methods generally index
 by *byte*, not *code unit*. When you do:
@@ -28,8 +28,8 @@ on string *return* byte indices too. So, for example, this does what you want:
     var hPosition = metalBand.indexOf("h")
     IO.print(metalBand[hPosition]) // "h"
 
-In general, methods on strings will work in terms of code units if they can do
-so efficiently, and will otherwise deal in bytes.
+In general, methods on strings work in terms of code units if they can do so
+efficiently, and otherwise deal in bytes.
 
 ## Static Methods
 
@@ -37,12 +37,12 @@ so efficiently, and will otherwise deal in bytes.
 
 Creates a new string containing the UTF-8 encoding of `codePoint`.
 
-It is a runtime error if `codePoint` is not an integer between `0` and
-`0x10ffff`, inclusive.
-
     :::dart
     String.fromCodePoint(8225) // "‡"
 
+It is a runtime error if `codePoint` is not an integer between `0` and
+`0x10ffff`, inclusive.
+
 ## Methods
 
 ### **byteAt**(index)