Unicorn RTD Provider: add module documentation

dev-docs/modules/unicornRtdProvider.md

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+---
+layout: page_v2
+title: Unicorn RTD Module
+display_name: Unicorn RTD Provider
+description: Measures each ad slot's on-screen position and viewability before the auction and injects it into ortb2Imp
+page_type: module
+module_type: rtd
+module_code: unicornRtdProvider
+enable_download: true
+sidebarType: 1
+---
+
+# Unicorn RTD Module
+
+## Overview
+
+Module Name: Unicorn Rtd Provider
+Module Type: Rtd Provider
+Maintainer: <service+prebid.js@bulbit.jp>
+
+This RTD module measures, for each ad slot, its on-screen position and
+viewability (visible area ratio) on the client before the auction starts, and
+injects the result into `adUnit.ortb2Imp` so it flows into the bid request. It
+is intended to be used together with the Unicorn Bid Adapter, which reads the
+values back and forwards them on the wire.
+
+The module measures:
+
+- the standard OpenRTB ad position `ortb2Imp.banner.pos`, per AdCOM 1.0 Placement Positions (2 = locked/fixed, 1 = above the fold, 3 = below the fold);
+- an object `ortb2Imp.ext.data.adslot` holding the slot's visibility ratio, a sticky/fixed flag, its document-relative position and its rendered size.
+
+Measurement runs once, on the animation frame after the DOM is ready, within the
+configured `auctionDelay`. No page-side timing wiring is required — the publisher
+just calls `requestBids()` as usual.
+
+## Integration
+
+Build the module together with the RTD core and the Unicorn Bid Adapter:
+
+```bash
+gulp build --modules=unicornBidAdapter,rtdModule,unicornRtdProvider
+```
+
+## Configuration
+
+This module is configured as part of the `realTimeData.dataProviders` object:
+
+```javascript
+pbjs.setConfig({
+  realTimeData: {
+    auctionDelay: 300,
+    dataProviders: [{
+      name: 'unicorn',
+      waitForIt: true
+    }]
+  }
+});
+```
+
+The submodule takes no `params`.
+
+{: .table .table-bordered .table-striped }
+| Name | Type | Description | Notes |
+| :--- | :--- | :--- | :--- |
+| name | String | Real time data module name | Required, always `'unicorn'` |
+| waitForIt | Boolean | Wait for the module before the auction | Recommended `true` |
+
+## Slot element resolution
+
+For each ad unit the module resolves the slot's DOM element id in this order:
+
+1. `ortb2Imp.ext.data.divId` — explicit override;
+2. the GPT slot mapping (`getSlotElementId`) — when the ad unit code differs from the div id;
+3. the ad unit code itself.
+
+Set `ortb2Imp.ext.data.divId` when the ad unit code is not the div id and GPT is
+not yet defined at auction time.
+
+## What the module injects
+
+{: .table .table-bordered .table-striped }
+| Field | Type | Unit / range | Meaning |
+| :--- | :--- | :--- | :--- |
+| `ortb2Imp.banner.pos` | int | AdCOM 1.0 Placement Position | 2 = locked (fixed), 1 = above the fold, 3 = below the fold |
+| `ortb2Imp.ext.data.adslot.ver` | int | — | signal schema version (currently `1`) |
+| `ortb2Imp.ext.data.adslot.ratio` | number | 0.0–1.0 | visible area ratio at measurement time |
+| `ortb2Imp.ext.data.adslot.fixed` | bool | — | slot is `position: fixed` / `sticky` |
+| `ortb2Imp.ext.data.adslot.x` | int | CSS px, document-relative | slot element left |
+| `ortb2Imp.ext.data.adslot.y` | int | CSS px, document-relative | slot element top |
+| `ortb2Imp.ext.data.adslot.w` | int | CSS px | slot element rendered width |
+| `ortb2Imp.ext.data.adslot.h` | int | CSS px | slot element rendered height |
+
+Coordinates are document-relative (page origin, independent of the scroll
+position) and expressed in CSS pixels.
+
+The Unicorn Bid Adapter forwards this object to the wire as `imp.ext.adslot`,
+and the position as `imp.banner.pos`.