Url parameters in path and query

Hi Thor,

describe param4 as not required

In OpenAPI, path parameters are always required. If a path parameter is optional, you need to define two paths - with and without that parameter:

paths:
  /api/v1/{param1}/{param2}/{param3}:
    ...
  /api/v1/{param1}/{param2}/{param3}/{param4}:
    ...

"param4" is subdivided in parameters. They serve more or less as filters. Sub parameters may be "begin", "end", "format" and others.
"begin" and "end" are e.g. unixtimestamps "format" could be "xml".

ourdomain.com/api/v1/param1/param2/param3/begin-1560730667,format-json

OpenAPI provides several serialization styles for path parameters, but there's no built-in style for dash-separated values inside a comma-separated list. The closest option is to define "param4" as a comma-separated array of strings and describe the possible prefixes and value format for each string:

openapi: 3.0.0
paths:
  /api/v1/param1/param2/param3/{param4}:
    get:
      parameters:
        - in: path
          name: param4
          required: true
          description: >
            A list of filters. Each filter is in the format
            `prefix-value`. The supported prefixes are:

             * `begin` and `end` - the value is a Unix timestamp.
             * `format` - the value can be `json` or `xml`.
             * ..
          schema:
            type: array
            items:
              type: string
            minItems: 1
            example:
              - begin-1560730667
              - format-json