input "maxlength" attribute counts grapheme clusters rather than code units

• Component: Forms
• Status: RESOLVED DUPLICATE

[Takao Baba]

Created attachment 436503 [details]
screenshot

Steps to reproduce:
1. Open https://jsbin.com/pujuyizuze/1/edit?html,output
2. Enter "👨‍👨‍👦".
  * Note: This is a character of one grapheme cluster, but has five Unicode code points (Man/ZWJ/Man/ZWJ/Boy). The "length" of this character is "8".

Expected behavior:
Just "👨‍" is pasted, then no more characters can be added.

Actual behavior:
Entire "👨‍👨‍👦" is pasted. Furthermore, totally three "👨‍👨‍👦" character can be input.

As the spec described, "maxlength" must address the "length", in other words "16-bit integers". Using grapheme cluster is incorrect.

https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#attr-fe-maxlength
> The "number of characters" is measured using length

https://infra.spec.whatwg.org/#string-length
> A string’s length is the number of code units it contains.

Other browsers such as Chrome, Firefox and Edge work correct.

[Alexey Proskuryakov]

This is intentional behavior, and changing it would be user hostile. Perhaps we need to follow up on standard changes mentioned in bug 120030.

*** This bug has been marked as a duplicate of bug 120030 ***