How to use multiple atlases with TextMeshPro?

I’m currently using a single atlas texture with TextMeshPro, and it works well. Below is the code I’m using. Now, I want to switch to using multiple atlases, but I haven’t been able to find a tutorial for it.

When creating the TMP_SpriteGlyph, there’s an atlasIndex field that seems to support multiple atlases. However, the tmpSpriteAsset.spriteSheet only appears to contain one atlas.

Has anyone had experience with this or can point me in the right direction?

tmpSpriteAsset.material = material;
tmpSpriteAsset.spriteSheet = spriteCharacterTexture2D;
tmpSpriteAsset.spriteGlyphTable.Clear();
tmpSpriteAsset.spriteCharacterTable.Clear();
for (int i = 0; i < characterRecords.Count; ++i)
{
    var glyph = new TMP_SpriteGlyph
    {
	      ……
        atlasIndex = 0,
    };


    tmpSpriteAsset.spriteGlyphTable.Add(glyph);
    var spriteCharacter = new TMP_SpriteCharacter
    {
        ……
    };

    tmpSpriteAsset.spriteCharacterTable.Add(spriteCharacter);
}

tmpSpriteAsset.UpdateLookupTables();