EPUB OPF规范：<manifest>下<item>元素ID大小写不同能否重复？

Great question! Let's break this down based on EPUB specifications and real-world implementation behavior:

• XML Specification Foundation: First, remember that OPF files are XML documents. XML treats id attributes as case-sensitive. That means id="Title" and id="title" are considered two distinct, unique identifiers from a strict XML perspective—so the example you provided would pass XML validation without issues.

• EPUB Rule Compliance: Both EPUB 2 and EPUB 3 standards require that every <item> in the <manifest> has a unique id. Since case-sensitive uniqueness counts here, your example with Title and title technically adheres to the EPUB specification.

• Critical Compatibility Caveat: While the specs allow this, real-world reader behavior can be tricky. Some older or less rigorously implemented EPUB readers might not properly handle case-sensitive id comparisons. This could lead to unexpected bugs—like incorrect resource resolution if other parts of the OPF (such as <spine> entries or <guide> references) accidentally mix up the case, or if the reader internally normalizes ids to lowercase/uppercase.

To avoid headaches, it's always a best practice to use fully unique identifiers that don't rely on case differences. Stick to ids like title-page and title-image instead—clear, unambiguous, and compatible across all readers.

Example from your question:

<manifest>
  <item id="Title" href="text/title.xhtml" media-type="application/xhtml+xml"/>
  <item id="title" href="images/title.jpg" media-type="image/jpeg"/>
</manifest>

This is technically valid per specs, but not recommended for broad compatibility.

内容的提问来源于stack exchange，提问作者user1932634