Clarify Actions number literal syntax

[kjanat]

Why:

Related to #43008.

The number-literal row says "Any number format supported by JSON", but the same page demonstrates hexadecimal (0xff), which JSON does not accept. Workflow authors and expression-tool implementers need an accurate description of the accepted syntax.

What's being changed:

Describe decimal integer and floating-point literals, exponent notation and hexadecimal literals explicitly, consistent with the examples already on the page.

Measurements and reproduction

On 14 September 2026, I reran the 44-expression corpus against GitHub Actions: 30 expressions were accepted and evaluated, and 14 were rejected by the expression parser with HTTP 422. The exact workflows, dispatch requests and responses, and successful-run logs are preserved.

The reference snapshot is tagged github-actions-expressions-of-concern. It contains:

• All recorded expressions and results, with a section for each case.
• Structured results.
• Exact workflows, responses, logs and captured source, with an internal SHA-256 manifest and an archive checksum.
• Reproduction instructions and the probe implementation.

For example, the measured 0x1F and 0o17 expressions both evaluate successfully, producing 31 and 15. Their uppercase-prefix counterparts, 0X1F and 0O17, are rejected. The complete table below lets reviewers inspect the accepted and rejected spellings together.

Service-side values were captured in run-name; runner-side values were captured through step environment variables. Both record the text returned by toJSON(). The capture used hosted Ubuntu runners with runner version 2.337.0. For -0, the service recorded 0 and the runner recorded -0; the other 29 accepted results agree.

All 44 expressions measured on 14 September 2026

Each evidence link points to the saved result under the reference tag.

Expression	Dispatch	Service toJSON()	Runner toJSON()	Saved evidence
+1	Accepted	1	1	literal-01
-0	Accepted	0	-0	literal-02
-1	Accepted	-1	-1	literal-03
-Infinity	Accepted	-Infinity	-Infinity	literal-04
.5	Accepted	0.5	0.5	literal-05
.5e1	Accepted	5	5	literal-06
0	Accepted	0	0	literal-07
0.1 + 0.2	Rejected (HTTP 422)	—	—	literal-08
00	Accepted	0	0	literal-09
0123	Accepted	123	123	literal-10
0B101	Rejected (HTTP 422)	—	—	literal-11
0O17	Rejected (HTTP 422)	—	—	literal-12
0X1F	Rejected (HTTP 422)	—	—	literal-13
0b101	Rejected (HTTP 422)	—	—	literal-14
0o17	Accepted	15	15	literal-15
0o8	Rejected (HTTP 422)	—	—	literal-16
0x01	Accepted	1	1	literal-17
0x0123	Accepted	291	291	literal-18
0x0e1	Accepted	225	225	literal-19
0x1F	Accepted	31	31	literal-20
0xG	Rejected (HTTP 422)	—	—	literal-21
1 + 1	Rejected (HTTP 422)	—	—	literal-22
1.	Accepted	1	1	literal-23
1.0e+	Rejected (HTTP 422)	—	—	literal-24
1.0e+99	Accepted	1E+99	1E+99	literal-25
1.5	Accepted	1.5	1.5	literal-26
1E+5	Accepted	100000	100000	literal-27
1_000	Rejected (HTTP 422)	—	—	literal-28
1e	Rejected (HTTP 422)	—	—	literal-29
1e+	Rejected (HTTP 422)	—	—	literal-30
1e+01	Accepted	10	10	literal-31
1e+5 == 100000	Accepted	true	true	literal-32
1e+5	Accepted	100000	100000	literal-33
1e-0	Accepted	1	1	literal-34
1e-5	Accepted	1E-05	1E-05	literal-35
1e01	Accepted	10	10	literal-36
1e0123	Accepted	1E+123	1E+123	literal-37
1e309	Rejected (HTTP 422)	—	—	literal-38
1e5	Accepted	100000	100000	literal-39
1e5e5	Rejected (HTTP 422)	—	—	literal-40
2147483648	Accepted	2147483648	2147483648	literal-41
9007199254740993	Accepted	9.00719925474099E+15	9.00719925474099E+15	literal-42
Infinity	Accepted	Infinity	Infinity	literal-43
NaN	Accepted	NaN	NaN	literal-44

Validation

• Reproduced all 44 expressions with retained evidence for every verdict.
• The documentation patch changes the number table cell.
• GitHub CI passed, including the documentation build, content lint, rendering and accessibility checks.

Check off the following:

• A subject matter expert (SME) has reviewed the technical accuracy of the content in this PR. In most cases, the author can be the SME. Open source contributions may require an SME review from GitHub staff.
• The changes in this PR meet the docs fundamentals that are required for all content.
• All CI checks are passing and the changes look good in the review environment.

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Table of review links

Note: Please update the URL for your staging server or codespace.

The table shows the files in the content directory that were changed in this pull request. This helps you review your changes on a staging server. Changes to the data directory are not included in this table.

Source	Review	Production	What Changed
actions/reference/workflows-and-actions/expressions.md	fpt ghec ghes@ 3.22 3.21 3.20 3.19 3.18 3.17	fpt ghec ghes@ 3.22 3.21 3.20 3.19 3.18 3.17

Key: fpt: Free, Pro, Team; ghec: GitHub Enterprise Cloud; ghes: GitHub Enterprise Server

🤖 This comment is automatically generated.

[Copilot]

🟡 Changes recommended

The documentation should also cover the accepted lowercase 0o octal syntax.

Get a fresh assessment by requesting another Copilot review.

Pull request overview

Updates GitHub Actions expression documentation to clarify supported number literal syntax.

Changes:

• Replaces the inaccurate JSON-based description.
• Documents decimal, floating-point, exponent, and hexadecimal literals.

File summaries

File	Summary
content/actions/reference/workflows-and-actions/expressions.md	Clarifies number literal syntax. Remaining nit (3 votes): include lowercase 0o octal literals.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 1
• Review effort level: Lite (auto)

Note

Copilot is running an experiment and ran this review at Lite.

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[janiceilene]

👋 @kjanat I'm going to triage this for the team to review, but since we don't have SME perspective on the issue yet, I'm not sure when we'll get this reviewed. Thanks for your patience!