The link input permits an action to happen once the content in the section is pressed. For example, you can press a button and it will go to whatever the link points to - a web page, open a form, submit a form or send an email, or open up a page or different section in the App. Here is the syntax that you type into the link field depending on what kind of action you want to happen.
Here are some Examples of the Syntax you can use for various link types.
To navigate to and show a section or page: show:label of section/page
To show a section or a page when a password is entered: show:label,password
Link to Web Page: http://www.xyz.com
Send an email: mailto:firstname.lastname@example.org
Send an email with subject: mailto:email@example.com?subject=subjectText
Send an email with subject and body: mailto:firstname.lastname@example.org?subject=subjectText&body=bodyText
Call on Telephone: tel:800-555-1212
Send a Text Message: sms:800-555-1212
To navigate to a page section: show:label-of-page
To display a dialog section: dialog:label-of-dialog
To display the default install dialog: show:installdialog
To download Gallery Images as Zip file: downloadgallery:gallerylabel
To download a file uploaded as a Resource: download:http://url-of-file
Downloads will work on browsers other than Safari and Internet Explorer. For Safari (IOS devices) and IE browsers, a new window will open. This is a current limitation of the browsers and once they come up to HTML5 standards, then the download feature will work. It's a good idea to add some text to instruct users to make sure they have opened the app in an alternative browser if you wish to utilize the download feature.
If you put %URL% as part of the link, it will get replaced with the URL of the app. if you put %ICON% as part of the link, it will get replaced with the URL of the icon image.