docs(gtm): add content grouping gotchas and RegEx Table reference

New section in common_issues.md covering:
- How RegEx Table content grouping works in GTM
- Common pitfall: new page paths falling to "Other"
- Gotcha: parallel Path/URL variables must stay in sync
- JHR content group category reference table
- Audit checklist for content grouping

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

custom-skills/60-gtm-audit/code/docs/common_issues.md

@@ -196,6 +196,87 @@ dataLayer.push({
 
 ---
 
+## Content Grouping Issues (RegEx Table Variables)
+
+### How Content Grouping Works in GTM
+
+Content grouping uses **RegEx Table** variables to categorize pages by URL/path patterns.
+The variable takes an input (typically `{{Page Path}}` or `{{Page URL}}`), tests it against
+an ordered list of regex patterns, and returns the first matching output value.
+If no pattern matches, it falls to the **Default Value** (usually "Other").
+
+**Key settings:**
+- **Full Matches Only**: OFF — partial regex match is sufficient
+- **Capture Groups and Replace**: OFF — output is the literal value, not a regex replacement
+- **Ignore Case**: ON — case-insensitive matching
+
+### New Page Paths Fall Through to "Other"
+
+**Symptoms**: New sections (campaigns, special events, landing pages) show as "Other" in GA4 content group reports.
+
+**Root cause**: The RegEx Table was built for the site's original URL structure. New paths like `/specialEvent/`, `/campaign/`, `/timesale/` don't match any existing pattern.
+
+**Example**: JHR site has `/specialEvent/landersshoppingfesta2026/teaser.do` but only `/package/` and `/event/` are in the regex table, not `/specialEvent/`.
+
+**Fix**: Add regex rule for the new path pattern. Place it BEFORE the default.
+
+**Gotcha — two variables to update**: Sites often have parallel content group variables:
+1. **Page Path based** (e.g., `(\/m)?\/specialEvent\/(.*)`) — for internal reports
+2. **Page URL based** (e.g., full URL with domain regex) — for cross-domain or subdomain tracking
+
+Both must be updated or they'll produce inconsistent groupings.
+
+### RegEx Pattern Conventions (JHR Example)
+
+Page Path patterns follow this structure:
+```
+(\/m)?\/section\/(.*)    →  Korean Category Label
+```
+- `(\/m)?` — optional mobile path prefix
+- `\/section\/` — the URL path segment to match
+- `(.*)` — match anything after
+
+Page URL patterns include domain matching:
+```
+^https\:\/\/(www|app|jpg|gjb|gjj|grp|\.)?josunhotel\.com(\/m)?\/section\/(.*)
+```
+- Multi-subdomain support via alternation group
+- Same `(\/m)?` mobile prefix handling
+
+### Content Group Categories (Hospitality Reference)
+
+| Pattern | Category (KR) | Category (EN) |
+|---------|---------------|---------------|
+| `/intro.do`, `/main.do` | 메인페이지 | Main Page |
+| `/about/`, `/press/` | 기업 소개 | Corporate Info |
+| `/hotel/` | 호텔 소개 | Hotel Info |
+| `/rooms/` | 객실 소개 | Room Info |
+| `/dining/` | 다이닝 이용 | Dining |
+| `/facilities/`, `/meeting/`, `/fitness/` | 부대시설 소개 | Facilities |
+| `/package/`, `/event/` | 이벤트 \| 패키지 조회 | Events & Packages |
+| `/specialEvent/`, `/timesale/`, `/campaign/` | 캠페인 \| 프로모션 | Campaign & Promotion |
+| `/activity/` | 액티비티 소개 | Activities |
+| `/step[0-4]` | 룸, 패키지 예약 프로세스 | Booking Process |
+| `/resve/dining/` | 다이닝 예약 프로세스 | Dining Booking |
+| `/membership/` | 멤버쉽 | Membership |
+| `/mypage/`, `/login/`, `/join/` | 웹회원 관련 | Member Portal |
+| `/retail/`, `/product/`, `/office/` | 리테일 관련 | Retail |
+| `/voc/`, `/customer/` | 고객지원 | Customer Support |
+| `/policy/` | 웹사이트 정책 | Website Policy |
+| `/upload_file/event/html/` | 캠페인 \| 프로모션 | Campaign & Promotion |
+| Default | Other | Other |
+
+### Audit Checklist for Content Grouping
+
+- [ ] Run `dtm var info <var_id>` to dump the full regex table
+- [ ] Check if new site sections have matching patterns
+- [ ] Verify both Path and URL variables are in sync
+- [ ] Check GA4 config tag references the correct variable
+- [ ] Test in GTM Preview: navigate to new page, check variable value
+- [ ] After update, verify in GA4 Realtime > Content Group report
+
+---
+
 ## Performance Issues
 
 ### Tags Slowing Page Load