FORMATS / IDENTIFIERS / METHODS
Documentary reference library
Find an identifier, unit, HTTP status or data convention, then open the method explaining its use and limits.
193 references · page 6 of 9
| Object to check | Code or notation | Context and use |
|---|---|---|
| Independent evaluation: splitting cases is not enough after answers influenced tuning | Holdout · fit / transform · Threshold selection · GroupKFold · TimeSeriesSplit · random_state | A score can be optimistic with correct formulas. scikit-learn distinguishes training, tuning and final evaluation. An agent has the same issue when instructions change after repeatedly inspecting a supposed generalization test. |
| Read Core Web Vitals thresholds without inventing a verdict | LCP · INP · CLS · p75 · COHORT · MISSING | LCP, INP and CLS describe three different dimensions of experience. Published thresholds classify a value; they do not turn an isolated test into a representative observation of every visitor. |
| CrUX: separate the window, scope and available observations | url / origin · formFactor · collectionPeriod · WINDOW · percentiles.p75 · ELIGIBILITY | A CrUX response describes an eligible population within a rolling window. Before comparing two p75 values, retain the requested key, devices and returned dates with the result. |
| Resource Timing: three sizes and several possible causes of zero | encodedBodySize · decodedBodySize · transferSize · CACHE · VISIBILITY · SERVICE WORKER | Encoded body size, decoded body size and the transfer indicator describe different objects. These rules come from the W3C Candidate Recommendation Draft of 1 September 2026, still undergoing standardization. |
| Navigation Timing: choose the right finishing boundary | DNS · CONNECT · RESPONSE START · BODY · DOM EVENT · DURATION | Navigation time is meaningful only with its start and end events. This reference follows the W3C Working Draft of 1 September 2026; the diagram shows logical order rather than measured durations. |
| Measure duration without mixing clocks | performance.now() · Date.now() · timeOrigin · DURATION · PRECISION · CROSS-CONTEXT | A date locates an event; a monotonic clock measures an interval. The High Resolution Time Working Draft of 1 September 2026 distinguishes these uses and execution contexts’ own origins. |
| Server-Timing: read what the server actually declares | name · dur · MISSING dur · desc · ORDER · TRAILER | The W3C Working Draft of 7 April 2026 lets a server expose named metrics. Its non-normative example below contains seven entries, including durations, descriptions and deliberately absent fields. |
| Base64: check alphabet, padding and unused bits | ALPHABET · base64url · QUANTUM · PADDING · PAD BITS · NON-ALPHABET | Base64 represents bytes using ASCII characters. It is neither encryption nor a digest: decoding recovers the data. The seven RFC 4648 vectors below are public references with no real secret. |
| HMAC: what a shared key changes | SHA-256 · HMAC-SHA-256 · KEY · RFC 4231 §4.2 · RFC 4231 §4.3 · PROVENANCE | An unkeyed digest and a keyed authentication code provide different information. Two RFC 4231 cases make the distinction verifiable with explicit test bytes. |
| HTTP digests: received content and representation can differ | Content-Digest · Repr-Digest · HEAD · 206 · Content-Encoding · AUTHENTICATION | Content-Digest and Repr-Digest cover different scopes. Three published exchanges from RFC 9530 Appendix B show why correct digests can differ without a change to the complete document. |
| Canonical JSON: a precise contract beyond sorted keys | INPUT · WHITESPACE · NUMBERS · PROPERTY ORDER · ARRAY ORDER · UNICODE | JCS, described in Informational RFC 8785, defines a deterministic representation for cryptographic operations. It is stricter than arbitrary JSON and more complete than removing spaces. |
| UTF-8 BOM: an invisible marker is still bytes | UTF-8 BOM · BYTE ORDER · POSITION · RAW BYTES · INVALID UTF-8 · BagIt 1.0 | An invisible character can affect a digest and a first field. Before editing a file, separate binary preservation, decoding and the receiving format’s rules. |
| BagIt: verify a file collection beyond a ZIP archive | bagit.txt · data/ · manifest-sha256.txt · tagmanifest-sha256.txt · Payload-Oxum · STATUS | BagIt 1.0, described by Informational RFC 8493, organizes payloads, metadata and manifests. It separates file presence from checksum verification without certifying document truth. |
| HTTP cache: separate storage, freshness and validation | max-age · s-maxage · no-cache · no-store · must-revalidate · Vary · Age · freshness_lifetime > current_age | A stored response is not necessarily reusable immediately. RFC 9111 separates freshness lifetime, response age and validation requirements. These are transport rules, not evidence that a page’s statements remain accurate. |
| Language tags: script, region and publication country are distinct | sr-Latn-RS · sr-Cyrl · zh-Hant · de-CH-1901 · es-419 · x-default | A BCP 47 tag identifies content language and may include script, region or a variant. It does not identify author nationality or server country. These examples come from RFC 5646; x-default is a separate hreflang convention. |
| WCAG 2.2: distinguish target size, focus and conformance level | 2.5.8 · 2.5.5 · 2.4.11 · 2.4.12 · 2.5.7 · 3.3.7 | State the WCAG version and intended level before assessing a journey. The numbers 24 and 44 refer to CSS pixels, not physical screen pixels. These checks alone do not establish overall conformance. |
| JSON-stat: locate a cell before interpreting its value | id · size · category.index · stride · offset · value / status | In a JSON-stat cube, dimension and category order define the meaning of a flattened value array. The official order.json example contains 24 demonstration cells, not economic observations. The last dimension changes fastest. |
| GeoJSON: inspect nesting before counting objects | Point · LineString · Polygon · LinearRing · MultiPolygon · GeometryCollection | Files with the same number of positions can describe different objects. Geometry type determines array depth. An interior hole is not another municipality, and repeating the closing position does not add a new vertex. |
| SPDX: read a license choice without inventing permission | MIT OR Apache-2.0 · MIT AND BSD-3-Clause · GPL-2.0-only WITH Classpath-exception-2.0 · LicenseRef-23 · MIT AND (Apache-2.0 OR BSD-3-Clause) · WITH > AND > OR | An SPDX expression combines identifiers and operators. Link the declaration to an exact version and scope: repository, package or file. These expressions illustrate syntax; they do not state this website’s license. |
| DNS: distinguish aliases, absence and resolution failure | CNAME · MX · TTL · NXDOMAIN · NODATA · SERVFAIL | A DNS answer concerns a name, requested type, resolver and time. It does not directly identify a company or legal website owner. Retain the full question and answer sections, not just the displayed IP address. |
| IPv4: identify special-purpose space before attributing ownership | 10.0.0.0/8 · 172.16.0.0/12 · 192.168.0.0/16 · 100.64.0.0/10 · 127.0.0.0/8 · 169.254.0.0/16 · 192.0.2.0/24 · 198.51.100.0/24 · 203.0.113.0/24 · 198.18.0.0/15 | These ten ranges come from IANA’s registry, consulted on 2026-10-22; its displayed update date is 2025-10-09. Counts include every address in each block, not usable hosts. An IP address alone establishes neither location nor legal identity. |
| Relative links: retain the base and resolution contract | g · /g · //g · ?y · #s · http:g | The same relative reference can identify different resources under different bases. RFC 3986 supplies 42 cases using http://a/b/c/d;p?q. These are standard examples, not observed websites. The reader compares strict RFC resolution with the browser’s URL parser. |
| UUID: read the version without certifying an identity | UUIDv1 · UUIDv3 · UUIDv4 · UUIDv5 · UUIDv6 · UUIDv7 · UUIDv8 | A UUID contains 128 bits. In the RFC 9562 variant, four bits indicate its version. The table reproduces published examples from Appendices A and B.1, not identifiers assigned here to companies or documents. |
| Population density: check the area in the denominator | SP.POP.TOTL · AG.LND.TOTL.K2 · AG.SRF.TOTL.K2 · EN.POP.DNST | Four countries and one observation year: this table preserves the 2023 WDI values retrieved on 23 October 2026. It supports checking a division before comparing territories. Population figures are midyear estimates, not counts taken on the retrieval date. |
From format to fact: three separate checks
Recognise the format
An identifier matching a pattern or checksum can still refer to the wrong entity. A format check catches typing errors; it does not verify the holder.
Find the right object
Open the corresponding register or document. Compare its name, scope, version and period with your question. Retain technical identifiers without translating them.
Qualify the conclusion
Separate what the source declares, what you observed and what remains unestablished. A value without a unit, period or definition cannot support a reliable comparison.
Notation examples explain a rule. They are neither certification nor a live check of your dossier.
Check documentary identifiers