in src/Microsoft.NuGet.Build.Tasks/Preprocessor.cs [100:111]
private static bool IsTokenCharacter(char c)
{
var category = CharUnicodeInfo.GetUnicodeCategory(c);
return category == UnicodeCategory.LowercaseLetter ||
category == UnicodeCategory.UppercaseLetter ||
category == UnicodeCategory.TitlecaseLetter ||
category == UnicodeCategory.OtherLetter ||
category == UnicodeCategory.ModifierLetter ||
category == UnicodeCategory.DecimalDigitNumber ||
category == UnicodeCategory.ConnectorPunctuation;
}