What is helium CLAUDE.md?

Version and behavior notes for Helium, a Go toolkit for reading, querying, validating, and transforming XML. XML is a text format commonly used for structured data and configuration; the notes cover XPath, XML Schema, Relax NG, XInclude, and Schematron.

Use it when coding or reviewing XML parsing, XPath queries, schema compilation, schema validation, or Schematron rules in a Go project.

It records which XML Schema versions are supported and how version selection works, reducing mistakes when validating XML documents.

How lestrrat-go/helium configures Claude Code

Reuse

Borrowing it

Nothing to install: this file belongs to lestrrat-go/helium. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file

curl -O https://raw.githubusercontent.com/lestrrat-go/helium/main/CLAUDE.md

Clone the repo

git clone --depth 1 https://github.com/lestrrat-go/helium

Made for: Claude Code.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/instructions/lestrrat-go/helium/claude-md/github.svg)](https://agentmods.dev/instructions/lestrrat-go/helium/claude-md)

Your own site

<a href="https://agentmods.dev/instructions/lestrrat-go/helium/claude-md"><img src="https://agentmods.dev/badge/instructions/lestrrat-go/helium/claude-md/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/instructions/lestrrat-go/helium/claude-md"><img src="https://agentmods.dev/badge/instructions/lestrrat-go/helium/claude-md.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 5,387 This file is loaded in full into every session.

When invoked 5,387 The same file — it is already loaded in full.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5.1	$0.05387	$0.05387
Opus 5.5	$0.02155	$0.02155
Sonnet 5.5	$0.01077	$0.01077
Haiku 4.5	$0.00539	$0.00539

Measured 1mo ago against content hash de6c399385f1, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

helium CLAUDE.md scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

CLAUDE.md · 247 lines

How it starts

The opening of the file, as written. The whole thing — 247 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Helium

XML toolkit for Go covering XML parsing, SAX2-style streaming, XPath 3.1, XInclude, XSD, Relax NG, and Schematron. Started as a libxml2-style port to Go and grew broader native Go APIs and features along the way.

XPath 3.1 — XSD Version

The xpath3 package targets XSD 1.1 only. This means +INF is a valid lexical form for xs:double and xs:float, and xs:dateTimeStamp is a recognized type. QT3 tests with dependency type="xsd-version" value="1.0" are skipped.

XSD — Version Toggle

The xsd package defaults to XSD 1.0 and treats 1.1 as opt-in via Compiler.Version(xsd.Version11) (or a vc:minVersion="1.1" hint on the root <xs:schema> when no explicit version is set). The resolved version is frozen onto the compiled Schema so the Validator applies the same semantics. 1.0 stays the default so existing behavior and goldens are unchanged.

resolveVersion (compile.go) resolves in order: a forced Compiler.Version() (always wins) → a vc:minVersion="1.1"-or-higher hint on the root → a configured Compiler.DefaultVersion(v) (the opt-in fallback for a schema silent on version) → Version10. DefaultVersion never overrides a forced version or a vc hint — it only chooses the fallback. The STANDALONE default stays Version10; DefaultVersion lets an embedding layer opt its schemas into 1.1 by default while still honoring an explicit version.

Validator.SkipDatatypeIntegrityChecks(true) suppresses the document-wide datatype-integrity walks in validateDocument (cfg.skipDatatypeIntegrity): the xs:ID/xs:IDREF/xs:IDREFS uniqueness+referential-integrity walk (version-INDEPENDENT — runs in both 1.0 and 1.1) and the XSD 1.1-only xs:ENTITY/xs:ENTITIES walk; content-model, type, and xs:key/unique/keyref identity-constraint validation are unaffected. It is for callers that validate an element/subtree as a fragment and enforce document-scope ID/IDREF integrity themselves (xslt3). In 1.0 it suppresses the ID/IDREF walk (the ENTITY walk never runs there).

Read the full file on GitHub · 247 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

1mo ago Changed · +4 lines · +112 tokens per session de6c399385f1
1mo ago Changed · +1 lines · +29 tokens per session 72f147d40c9e
1mo ago Changed · +21 tokens per session c5749cbc90f3
2mo ago First seen · 242 lines · 5,225 tokens per session scan A 43018c7bf8f6

Subscribe to this mod's changes

helium CLAUDE.md is an instructions file published in the GitHub repository lestrrat-go/helium (69 stars, last pushed 9d ago), licensed MIT. It adds 5,387 tokens to every session, about $0.0215 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

Backend and APIs Go Languages relaxng schematron xinclude xml xpath xsd

helium CLAUDE.md next to 6 instructions from other repositories
Mod	Type	Stars	Last push	Licence	Scan	Tokens	Works with
helium CLAUDE.mdlestrrat-go/helium	Instructions file	69	9d ago	MIT	A	5,387	Claude Code
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next.js AGENTS.mdvercel/next.js	Instructions file	143k	yesterday	MIT	A	7,461	Codex, OpenCode
langchain AGENTS.mdlangchain-ai/langchain	Instructions file	149k	yesterday	MIT	A	4,680	Codex, OpenCode
vscode oss-third-party-notices.instructions.mdmicrosoft/vscode	Instructions file	195k	yesterday	MIT	A	5,516	GitHub Copilot
vscode copilot-instructions.mdmicrosoft/vscode	Instructions file	195k	yesterday	MIT	A	3,093	GitHub Copilot
deepseek-harness AGENTS.mddeepseek-ai/deepseek-harness	Instructions file	274k	2d ago	MIT	A	4,313	Codex, OpenCode

helium: Instructions file for Claude Code