feat: add iframe support (#143)

* feat: add iframe support

* add comment

README.md

@@ -235,6 +235,23 @@ By default, mark provides several built-in templates and macros:
 
   See: https://confluence.atlassian.com/doc/children-display-macro-139501.html
 
+* template: `ac:iframe` to include iframe macro (cloud only)
+  - URL: URL to the iframe.
+  - Frameborder: Choose whether to draw a border around content in the iframe.
+      - `show` (Default)
+      - `hide`
+  - Width: Width in px. Defualts to "640px"
+  - Height: Height in px. Defualts to "360px"
+  - Scrolling: Allow or prevent scrolling in the iframe to see additional content.
+      - `yes`
+      - `no`
+      - `auto` (Default)
+  - Align: Align the iframe to the left or right of the page.
+      - `left` (Default)
+      - `right`
+
+  See: https://support.atlassian.com/confluence-cloud/docs/insert-the-iframe-macro
+
 * macro `@{...}` to mention user by name specified in the braces.
 
 ## Template & Macros Usecases

pkg/mark/stdlib/stdlib.go

@@ -210,6 +210,19 @@ func templates(api *confluence.API) (*template.Template, error) {
 			`</ac:structured-macro>{{printf "\n"}}`,
 		),
 
+		/* https://support.atlassian.com/confluence-cloud/docs/insert-the-iframe-macro/ */
+
+		`ac:iframe`: text(
+			`<ac:structured-macro ac:name="iframe">{{printf "\n"}}`,
+			`<ac:parameter ac:name="src"><ri:url ri:value="{{ .URL }}" /></ac:parameter>{{printf "\n"}}`,
+			`{{ if .Frameborder}}<ac:parameter ac:name="frameborder">{{ .Frameborder }}</ac:parameter>{{printf "\n"}}{{end}}`,
+			`{{ if .Scrolling}}<ac:parameter ac:name="id">{{ .Scrolling }}</ac:parameter>{{printf "\n"}}{{end}}`,
+			`{{ if .Align}}<ac:parameter ac:name="align">{{ .Align }}</ac:parameter>{{printf "\n"}}{{end}}`,
+			`<ac:parameter ac:name="width">{{ or .Width "640px" }}</ac:parameter>{{printf "\n"}}`,
+			`<ac:parameter ac:name="height">{{ or .Height "360px" }}</ac:parameter>{{printf "\n"}}`,
+			`</ac:structured-macro>{{printf "\n"}}`,
+		),
+
 		// TODO(seletskiy): more templates here
 	} {
 		templates, err = templates.New(name).Parse(body)