The amount of the extra spacing between Chinese/Japanese and Western text

While the CLREQ (Chinese Layout Requirements) doesn’t mention the extra spacing between CJK and Western text directly, or a single, specific value for it, it does discuss options like 1/4-em or 1/8-em.

In issue #401:

In Chinese and Japanese composition, it is usually recommended to apply extra spacing between Chinese/Japanese han/kana characters and certain other types of text to make the text read better. The gap is typically used between han/kana characters and Latin letters, numbers, or punctuation, and should be smaller than an ASCII space would be.

Currently, 1/8-em seems to be a popular choice in modern digital text, as 1/4-em can feel too large or abrupt.

However, this raises a complex issue when the Western text itself contains multiple words (and thus, at least an internal ASCII space). Consider this example:

这是w3c clreq规范。

In this sentence, ‘w3c clreq’ should be read and perceived as a single conceptual block. My concern is: if the CJK-Latin autospacing (e.g., 1/8-em) is smaller than the internal ASCII space between ‘w3c’ and ‘clreq’, could it visually break the phrase? This might cause the sentence to be misread as two separate entities: ‘[这是w3c]’ and ‘[clreq规范]’, which is undesirable.

Historically, 1/4-em spacing is more common in physical print. And while the current css4-text specification notes that text-autospace is intended to create 1/8-em spacing, it also states in the inter-script-spacing section that a future level may introduce more control over the amount of spacing.

Given this conflict, is it necessary for specifications to mention the spacing and the different amounts of extra spacing specifically?

Read the discussion in issue #401 and the CSS Text Level 4 sections on text-autospace and inter-script-spacing first. Determine whether CLREQ should specify the extra spacing amount or its relationship to internal ASCII spaces, and document the agreed requirement in the appropriate specification section.