Function parse

parse(content: string): { retain: boolean }
Parser for retain tags - defines MQTT retain flag

This parser handles the retain tag that defines whether MQTT messages should be retained by the broker. It extracts:
- Retain flag (true or false)
- Validates boolean value
Parameters
- content: string
  Raw content from the retain tag
Returns { retain: boolean }
Parsed retain information or null if parsing fails
Example: Retain enabled
```
// Input: "true"
// Output: { retain: true }
```
Example: Retain disabled
```
// Input: "false"
// Output: { retain: false }
```
Example: Alternative boolean values
```
// Input: "1" or "yes" or "on"
// Output: { retain: true }
// Input: "0" or "no" or "off"
// Output: { retain: false }
```
Since
4.1.0

Public
- Defined in core/parsers/mqtt_retain.ts:36