Update raw-string.md (#40869)

Extra Info about string literals

docs/csharp/language-reference/tokens/raw-string.md

@@ -21,6 +21,7 @@ The following rules govern the interpretation of a multi-line raw string literal
 - Any whitespace to the left of the closing quotes is removed from all lines of the raw string literal.
 - Whitespace following the opening quote on the same line is ignored.
 - Whitespace only lines following the opening quote are included in the string literal.
+- If a whitespace precedes the end delimiter on the same line, the exact number and kind of whitespace characters (e.g. spaces vs. tabs) must exist at the beginning of each content line. Specifically, a space does not match a horizontal tab, and vice versa.
 
 You may need to create a raw string literal that has three or more consecutive double-quote characters. Raw string literals can start and end with a sequence of at least three double-quote characters. When your string literal contains three consecutive double-quotes, you start and end the raw string literal with four double quote characters:
 
@@ -32,6 +33,8 @@ If you need to start or end a raw string literal with quote characters, use the
 
 Raw string literals can also be combined with [interpolated strings](./interpolated.md#interpolated-raw-string-literals) to embed the `{` and `}` characters in the output string. You use multiple `$` characters in an interpolated raw string literal to embed `{` and `}` characters in the output string without escaping them.
 
+The raw string literal's content must not contain a set of contiguous `"` characters whose length is equal to or greater than the raw string literal delimiter length. For example, the strings `"""" """ """"` and `""""""" """""" """"" """" """ """""""` are well-formed. However, the strings `""" """ """` and `""" """" """` are ill-formed
+
 Raw string literals were introduced in C# 11.
 
 ## See also