String.StartsWith not Working when next character is the Prime Symbol (char)697

Question

I am trying to use a string with the Prime symbol in it, but I am having some issues with the String.StartsWith method. Why is the following code throwing the exception?

string text_1 = @"123456";
string text_2 = @"ʹABCDEF";

string fullText = text_1 + text_2;
if (!fullText.StartsWith(text_1))
{
    throw new Exception("Unexplained bad error.");
}

I suspect that the issue is because this Prime symbol (char)697 is being treated as an accent and so is changing the letter before it. (I don't think it should be - it should be the the prime symbol and so should not be changing the numerical numbers in front of it). I am not exactly sure how to go about testing this. I did try the method proposed in this answer but it returned false:

IsLetterWithDiacritics(text_1[5]) //  == False
IsLetterWithDiacritics(fullText[5]) // == False
IsLetterWithDiacritics(fullText[6]) // == False

Thanks for any help.

Answer 1

ʹ or MODIFIER LETTER PRIME is a spacing modifier letter. It's not a true character but a special use symbol that modifies the preceding character.

From MSDN:

A modifier letter is a free-standing spacing character that, like a combining character, indicates modifications of a preceding letter.

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string.StartsWith is returning false because in your concatenated string, the 6 is actually modified by the prime symbol that is appended after it.