Camel Case and Title Case with smart word boundaries for C#

NamingHelpers.cs

using System.Globalization;
using System.Text.RegularExpressions;

namespace MongoDB.EntityFrameworkCore;

/// <summary>
/// A variety of helper methods for creating names.
/// </summary>
public static partial class NamingHelperMethods
{
    /// <summary>
    /// Converts a given string to camel case.
    /// </summary>
    /// <param name="input">The input string to convert.</param>
    /// <param name="culture">The culture to use in upper-casing and lower-casing letters.</param>
    /// <returns>The cleaned camel-cased string.</returns>
    /// <remarks>Word boundaries are considered spaces, non-alphanumeric, a transition from
    /// lower to upper, and a transition from number to non-number.</remarks>
    public static string ToCamelCase(this string input, CultureInfo culture)
    {
        if (string.IsNullOrEmpty(input)) return input;

        string[] words = WordSplitRegex().Split(input);

        char[] result = new char[input.Length];
        int outIndex = 0;

        for (int inIndex = 0; inIndex < words.Length; inIndex++)
        {
            string w = words[inIndex];
            if (w.Length == 0) continue;

            if (inIndex == 0)
            {
                result[outIndex] = char.ToLower(w[0], culture);
            }
            else
            {
                result[outIndex] = char.ToUpper(w[0], culture);
            }
            w.ToLower(culture).CopyTo(1, result, outIndex + 1, w.Length - 1);

            outIndex += w.Length;
        }

        return new string(result, 0, outIndex);
    }

    /// <summary>
    /// Converts a given string to title case.
    /// </summary>
    /// <param name="input">The input string to convert.</param>
    /// <param name="culture">The culture to use in upper-casing and lower-casing letters.</param>
    /// <returns>The cleaned title-cased string.</returns>
    /// <remarks>Word boundaries are considered spaces, non-alphanumeric, a transition from
    /// lower to upper, and a transition from number to non-number.</remarks>
    public static string ToTitleCase(this string input, CultureInfo culture)
    {
        if (string.IsNullOrEmpty(input)) return input;

        string[] words = WordSplitRegex().Split(input);

        char[] result = new char[input.Length];
        int outIndex = 0;

        for (int inIndex = 0; inIndex < words.Length; inIndex++)
        {
            string w = words[inIndex];
            if (w.Length == 0) continue;

            result[outIndex] = char.ToUpper(w[0], culture);
            w.ToLower(culture).CopyTo(1, result, outIndex + 1, w.Length - 1);

            outIndex += w.Length;
        }

        return new string(result, 0, outIndex);
    }

    // Find word boundaries.
    // Word boundaries are considered spaces, non-alphanumeric, a transition from lower to upper,
    // and a transition from number to non-number.
    [GeneratedRegex(@"(?<=\p{Ll})(?=\p{Lu})|[\s\p{P}]|(?<=\p{Lu}{2,})(?=\p{Ll})|(?<=\p{N})(?=\P{N})")]
    private static partial Regex WordSplitRegex();
}