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BpeSplitStep

A Split step ahead of ByteLevel, as a Llama-3 or Qwen2 file declares one.

public sealed record BpeSplitStep

Properties — Pattern is the regex. Behavior is the SplitBehavior applied to what it matches. Invert splits on what the pattern does not match instead.

Example — the step a Llama-3 file puts before ByteLevel.

using Lodestar.Embeddings.Tokenization;

var step = new BpeSplitStep(BpePatterns.Llama3, SplitBehavior.Isolated, Invert: false);

bool inverted = step.Invert;  // => False

Remarks — stock GPT-2 declares a bare ByteLevel pre-tokenizer with no Split in front of it. A Llama-3 or Qwen2 file declares a Sequence of Split then ByteLevel, and the Split's behaviour decides what happens to the text between matches — which is the whole reason this type exists rather than a bare pattern string.

Invert reads oddly and is what several shipped files use: it is easier to write a pattern for the text you want to keep than for the delimiters you want to cut on.

Where a model declares none, BpeVocabulary.PreSplit is null, and that is different from declaring one that matches nothing.

Applies to — net10.0, netstandard2.0.

See also — SplitBehavior, BpeVocabulary.