Adding the default fallback requirement

diff --git a/README.md b/README.md
index ebc1f1b822357caadfdf16ac61c3126daee8fda3..6047534a4d4cbff5a6bd8ac5b602a1b8f15c2f7e 100644 (file)
--- a/README.md
+++ b/README.md
@@ -27,12 +27,13 @@ When the registry is updated here, a line like `axisregistry/axis_name.textproto
 *   `precision`
     *   Describes the specificity at which an axis position can be specified.
         For example, `0` means values must be specified as whole numbers while `-1` means values can be as precise as one decimal place.
-*   `fallback` (repeated)
+*   `fallback`
     *   Instance positions along the axis, such as wght 100,200,300,400,500,600,700,800,900.
     *   A cross-product of fallback positions along all supported axes is created to support legacy browsers that lack variable font support.
         For axes with CSS3 properties (such as [font-weight](https://drafts.csswg.org/css-fonts-3/#font-weight-prop)), the positions accessible
         to CSS3 should be specified. For axes lacking CSS3 properties a legacy browser is limited to a single position and that position must
         be at a fallback.
+        <br>In case an axis doesn't include predefined positions, it is mandatory to define at least one fallback position. It should be called `Default` and its value should correspond to the `default_value` position of the axis.
 *   `fallback_only`
     *   Describes whether to only use fallback values when presenting to users.
 *   `description`