# Parameter :: 17. `topic::`
Session topic name appended as a `-{name}` suffix to the base directory path.
**Type:** [`TopicName`](../type/13_topic_name.md)
**Fundamental Type:** String (identifier)
**Constraints:**
- Must be non-empty when provided
- Must not contain `/`
- Do NOT include a leading `-` in the value — it is added automatically
- Error on empty: `"topic must be non-empty"`
- Error on slash: `"topic must not contain path separators"`
**Default:** unset (no suffix applied) for `.project.path`, `.project.exists`; `default_topic` for `.session.dir`, `.session.ensure`
**Commands:** `.project.path`, `.project.exists`, `.session.dir`, `.session.ensure`
**Purpose:** Identifies a named session topic within a base directory. Claude Code uses hyphen-prefixed directories (`-default_topic`, `-work`, `-commit`) as session working directories. `topic::` takes the name without the leading hyphen and appends it as `{base}/-{topic}`.
**Examples:**
```bash
# Valid values
topic::default_topic # → appended as /-default_topic
topic::work # → appended as /-work
topic::commit # → appended as /-commit
# Invalid values
topic:: # "topic must be non-empty"
topic::my/topic # "topic must not contain path separators"
topic::-default_topic # (legal — creates /-default_topic... but convention is without leading -)
```
### Referenced Type
| [`TopicName`](../type/13_topic_name.md) | String (identifier) | String | Non-empty; no `/` characters; no leading `-` |
### Referenced Commands
| 8 | [`.project.path`](../command/08_project_path.md) | unset | Appends `-{topic}` suffix to computed storage path |
| 9 | [`.project.exists`](../command/09_project_exists.md) | unset | Checks storage path with topic suffix |
| 10 | [`.session.dir`](../command/10_session_dir.md) | `default_topic` | Appends `-{topic}` to base directory |
| 11 | [`.session.ensure`](../command/11_session_ensure.md) | `default_topic` | Appends `-{topic}` to base directory |
### Referenced User Stories
| 2 | [Find Past Conversation](../user_story/002_find_past_conversation.md) | developer |
| 5 | [Resume Claude Session](../user_story/005_resume_claude_session.md) | developer |