bpmn-io/bpmn-js

Alignment tools for labels don't work inside of participant/lane

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#2371 opened on Dec 22, 2025

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buggood first issuemodelingspring cleaning

Description

Describe the Bug

Alignment helpers (snap lines) for external labels show outside of participant, but not within participant / lane:

Image

Steps to Reproduce

  • Align external label with Gateway/Event outside of participant
    • See that label target is "peer" used for horizontal center alignment
  • Align external label with Gateway/Event inside of participant
    • See that label target is not accounted as "peer", and no assistance is given

Can be reproduced on demo.bpmn.io.

Expected Behavior

Same behavior, independent of the modeling context.

Environment

  • Browser: Chrome 148
  • OS: Any (Linux, Ubuntu 24)
  • Library version: v18.9.1 / demo.bpmn.io

Contributor guide

Tech stack
javascripthtmlcss
Domain
frontend
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
JavaScriptBPMN modeling concepts
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
65
Research direction
Focus on the alignment helper logic in the modeling module. Examine how external labels interact with the snap lines feature, particularly the selection of 'peer' targets. Compare behavior of labels inside participant/lane versus outside. Review comments on the issue for any additional insights or maintainer input.