The text-combine-upright CSS property sets the combination of characters into the space of a single character. If the combined text is wider than 1em, the user agent must fit the contents within 1em. The resulting composition is treated as a single upright glyph for layout and decoration. This property only has an effect in vertical writing modes.
non-replaced inline elements
There is no special processing.
Attempts to typeset all consecutive characters within the box horizontally, such that they take up the space of a single character within the vertical line of the box.
Attempts to display a sequence of consecutive ASCII digits (U+0030–U+0039) that has as many or fewer characters than the specified integer, such that it takes up the space of a single character within the vertical line box. If the integer is omitted, it computes to 2. Integers outside the range of 2-4 are invalid.