https://learn.microsoft.com/ja-jp/dotnet/api/system.text.regularexpressions.regexrunner.isboundary?view=netframework-4.8.1&viewFallbackFrom=net-8.0
RegexRunner.IsBoundary(Int32, Int32, Int32) Method (System.Text.RegularExpressions) | Microsoft...
Used by a Regex object generated by the CompileToAssembly method.
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