After you have opened a screen in the Screen editor, right-clicked (the border of) an HTML field on it and chose Properties in the pop-up menu, the Screen object properties window opens. On the Data tab in that window, you specify the data dictionary field tag, its repeatability on screen and the read/write access permission to be used by this control. HTML fields are supported by Axiell Collections.

Click here for information on how to edit screen object properties in general. And click here to read about how to manage labels in the Screen editor.
On the current tab you'll find the following settings:

Tag

Fill in the existing data dictionary tag for this screen field. The data type of that field has to be HTML.
Note that tags are case sensitive.

Repeatability

Choose whether this field may be Repeated, Not Repeatable, or Repeatable, values must be unique. Repeated screen fields can have more than one occurrence, whilst Not Repeatable can only have one. With Repeated, value must be unique every occurrence must be different from the others for the same field.

Access

When the screen itself is editable, you can still specify for individual entry fields that they are not editable, by choosing Read only for this property. This will apply to all users. Leave the setting to Read and write if users with the proper access rights must be able to enter data into the field.

Text

If this HTML field is repeatable and you'd like it to have a label that repeats along with the field, then add the text translations for such a label here. This label will be shown in the left upper corner automatically.
Note that in this respect HTML fields are different from normal fields. When you add a normal field to a screen, two boxes are added, one for the label translations and one for the field tag and its properties. You can position that label box freely with respect to the field box but there's an invisible connection between the two, making them repeatable as a pair. When you add an HTML field to a screen though, you won't get a label box as with a normal field, so that's what this Text property is for. This Text property wasn't always available though, so previously you had to add a single label box (without a field box) near the HTML field to provide it with a label, but since there's no connection between such a separately placed label box and the HTML field box, you can't have them repeated together so this is only good for non-repeatable HTML fields.