The CSS Paged Media Module Level 3 spec includes a list of page size names that may be used in the "size" property of the @page rule. Among these are two names for Japanese Industrial Standard page sizes which are currently not being recognized by Chrome: “JIS-B5” refers to JIS B5 size (182mm wide by 257mm high) “JIS-B4” refers to JIS B4 size (257mm wide by 364mm high) This feature completes the implementation of this section of the standard by adding support for these two page size.
The detailed description of bug 1047642 links to some related discussions and documents. Chromium's implementation of the “size” property follows a now-obsolete version of the spec which didn't include the Japanese JIS B4 and JIS B5 paper sizes. Those were added later on following demand from Japanese users: The B4 and B5 sizes included are very confusing for Japanese users, as they are defined as ISO B4 (250×353mm) and ISO B5 (176×250mm), different from the JIS-B4 (257×364mm) and JIS-B5 (182×257mm) commonly used in Japan. [www-style@w3c.org archives] We need jis-b5 and jis-b4 only because (ISO) b5 and b4 are already defined and those would confuse Japanese users.
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