docs(embed): review pass before the release

- the link to va-messaging.service.ts opened with a backtick and closed with a
  quote, so it rendered as broken text
- the URL example was a plain URL wrapped in backticks inside a fenced block,
  which shows the backticks; it is a text fence with the bare URL now
- restored the space the "updated- all from inside the same report" sentence lost
- closed the sentence about brush columns, and spelled out "primary key columns"
- two causes the banner reports were missing from the table: an entry with no
  parameter before the "-", and a parameter mapped to two columns (the first
  entry wins). Both come from parseVaParmap, so the table now covers every
  message the banner can carry.

Checked against the merged code on release/7.20 (00df87f): the embed values and
their effects, the split at the last hyphen, the case-insensitive label match,
the plain-SAS-name rule, the anchor and period names, and the banner wording.
Tables are consistent, fences balanced, page is ASCII only, and both cross-links
(/filter/ and /developer-guide/browser-variables/) resolve.

docs/embed-va.md

@@ -6,16 +6,14 @@ description: Embed the Data Controller editor inside a SAS VA report as a data-d
 
 # Embedding inside SAS Visual Analytics
 
-Data Controller can be embedded inside a SAS Visual Analytics report as a **data-driven content** (DDC) object.  This unlocks scenarios where a user can safely modify the values in an underlying SAS table, and have the visualisation updated- all from inside the same report.
+Data Controller can be embedded inside a SAS Visual Analytics report as a **data-driven content** (DDC) object.  This unlocks scenarios where a user can safely modify the values in an underlying SAS table, and have the visualisation updated - all from inside the same report.
 
 ## URL
 
 Open the editor as a DDC by appending `?embed=va` to the editor route:
 
-```
-
-`https://yourserver/DC/#/editor/<library>/<table>?embed=va`
-
+```text
+https://yourserver/DC/#/editor/<library>/<table>?embed=va
 ```
 
 The `?embed=` parameter accepts three values:
@@ -46,11 +44,11 @@ VA pushes a JSON payload to the iframe via `window.postMessage` whenever the sel
 
 1. Resolves each VA `parameter` to a DC column by matching on column label.
 2. Builds a filter (using existing [Filter](/filter/) machinery) over the selected values.
-3. Hides any VA columns marked as `brush` so the grid stays focused on the user-editable columns (except primary key cols which are always shown)
+3. Hides any VA columns marked as `brush` so the grid stays focused on the user-editable columns (primary key columns are always shown).
 
 If VA sends an empty / unmatched message the editor falls back to the unfiltered view but stays in VA mode.
 
-More logic available in [`va-messaging.service.ts'](https://git.datacontroller.io/dc/dc/src/branch/main/client/src/app/services/va-messaging.service.ts).
+More logic available in [`va-messaging.service.ts`](https://git.datacontroller.io/dc/dc/src/branch/main/client/src/app/services/va-messaging.service.ts).
 
 ## Mapping parameters to columns
 
@@ -100,6 +98,8 @@ Each line names one cause, and the parameter it concerns is skipped rather than
 | `a range needs one value` | a `RANGE` mapping was sent several values - one `BETWEEN` carries one period |
 | `N of its M values was not a date` | part of a multi-value parameter could not be read as a date, so only the rest is applied |
 | `was ignored: it needs a "-"` / `is not a transform` | the entry itself is malformed |
+| `the VA parameter name is missing` | the entry starts with the `-`, so there is no parameter to map |
+| `already maps to <COLUMN>, and a parameter can filter only one column` | the same parameter is mapped twice; the first entry wins |
 
 The banner is shown to the report author, inside the report, because that is where the entry is edited: the only fix available from the editor is to change the `va_parmap` entries in the URL of the Data Controller object.