EPUB 3.3 EPUB 3.3 （英语）

Manifest fallbacks are a feature of the package document that create a manifest fallback chain for a publication resource, allowing reading systems to select an alternative format they can render.
清單回退是包文檔的一項功能，它為發佈資源創建清單回退鏈，允許閱讀系統選擇它們可以呈現的替代格式。

Fallback chains are created using the fallback attribute on manifest item elements. This attribute references the ID [xml] of another manifest item that is a fallback for the current item. The ordered list of all the references that a reading system can reach, starting from a given item's fallback attribute, represents the full fallback chain for that item. This chain also represents the EPUB creator's preferred fallback order.
回退鏈是使用清單 item 元素上的 fallback 屬性創建的。此屬性引用另一個清單的 ID [ xml] item ，該清單是當前 item .從給定 item 的 fallback 屬性開始，讀取系統可以訪問的所有引用的有序清單表示該 item 引用的完整回退鏈。此鏈還表示 EPUB 建立者的首選回退順序。

There are two cases for manifest fallbacks:
清單回退有兩種情況：

Spine fallbacks 脊柱回退

EPUB creators MUST specify a fallback chain for a foreign content document to ensure that reading systems can always render the spine item. In this case, the chain MUST contain at least one EPUB content document.
EPUB 建立者必須為外部內容文檔指定回退鏈，以確保閱讀系統始終可以呈現主幹專案。在這種情況下，鏈必須包含至少一個 EPUB 內容文件。

EPUB creators MAY provide fallbacks for EPUB content documents (e.g., to provide a fallback for scripted content).
EPUB 建立者可以為 EPUB 內容文件提供回退（例如，為腳本內容提供回退）。

When a fallback chain includes more than one EPUB content document, EPUB creators can use the properties attribute to differentiate the purpose of each.
當回退鏈包含多個 EPUB 內容文件時，EPUB 建立者可以使用該 properties 屬性來區分每個文檔的用途。

Content fallbacks 內容回退

Note 注意

The original purpose for content fallbacks was to specify fallback images for the [html] img element. As HTML now has intrinsic fallback mechanism for images, the use of content fallbacks is strongly discouraged. EPUB creators should always use the intrinsic fallback capabilities of [html] and [svg] to provide fallback content.
內容回退的最初目的是為 [ html] img 元素指定回退圖像。由於 HTML 現在具有圖像的內在回退機制，因此強烈建議不要使用內容回退。EPUB 建立者應始終使用 [ html] 和 [ svg] 的固有回退功能來提供回退內容。

EPUB creators MUST provide a content fallback for foreign resources when the elements that reference them do not have intrinsic fallback capabilities. In this case, the fallback chain MUST contain at least one core media type resource.
當引用 EPUB 的元素不具有內在回退功能時，EPUB 建立者必須為外部資源提供內容回退。在這種情況下，回退鏈必須包含至少一個核心媒體類型資源。

EPUB creators MAY also provide manifest fallbacks for core media type resources (e.g., to allow reading systems to select from more than one image format).
EPUB 建立者還可以為核心媒體類型資源提供清單回退（例如，允許閱讀系統從多種圖像格式中進行選擇）。

Regardless of the type of manifest fallback specified, fallback chains MUST NOT contain self-references or circular references to item elements in the chain.
無論指定的清單回退類型如何，回退鏈都不得包含對 item 鏈中元素的自引用或迴圈引用。

The following sections provide additional clarifications about the intrinsic fallback requirements of specific elements.
以下各節提供了有關特定元素的內在回退要求的其他說明。

The virtual file system for the OCF abstract container MUST have a single common root directory for all the contents of the container.
OCF 抽象容器的虛擬文件系統必須具有容器所有內容的單個公共根目錄。

The OCF abstract container MUST include a directory for configuration files named META-INF that is a direct child of the container's root directory. Refer to 4.2.6 META-INF directory for the requirements for the contents of this directory.
OCF 抽象容器必須包含一個名為 META-INF 容器根目錄的直接子目錄的配置文件目錄。有關此目錄內容的要求，請參閱 4.2.6 META-INF 目錄。

The file name mimetype in the root directory is reserved for use by OCF ZIP containers, as explained in 4.3 OCF ZIP container.
根目錄中的檔名 mimetype 保留供 OCF ZIP 容器使用，如 4.3 OCF ZIP 容器中所述。

Files in the META-INF directory and the mimetype file are not publication resources so MUST NOT be listed in the manifest.
META-INF 目錄中的文件和 mimetype 檔不是發佈資源，因此不得在清單中列出。

EPUB creators MAY locate all other files within the OCF abstract container in any location descendant from the root directory, provided they are not within the META-INF directory. EPUB creators MUST NOT reference files in the META-INF directory from an EPUB publication.
EPUB 建立者可以在根目錄的任何位置找到 OCF 抽象容器中的所有其他檔，前提是它們不在目錄中 META-INF 。EPUB 建立者不得引用 EPUB 出版物目錄 META-INF 中的檔。

In the context of the OCF abstract container, file paths and file names are scalar value strings [infra] (i.e., their values are case sensitive).
在 OCF 抽象容器的上下文中，檔路徑和檔名是標量值字串 [ infra]（即，它們的值區分大小寫）。

In addition, the following restrictions are designed to allow file paths and file names to be used without modification on most operating systems:
此外，以下限制旨在允許在大多數作業系統上使用檔路徑和檔名而無需修改：

• File names MUST NOT exceed 255 bytes.
  檔名不得超過 255 個字節。

• The file paths for any directory or file within the OCF abstract container MUST NOT exceed 65535 bytes.
  OCF 抽象容器中任何目錄或文件的檔路徑不得超過65535位元組。

• File names MUST NOT use the following [unicode] characters, as commonly used operating systems may not support these characters consistently:
  檔名不得使用以下 [ unicode] 字元，因為常用的作業系統可能無法一致地支持這些字元：

  • SOLIDUS: / (U+002F)
    固相線： / （ U+002F ）

  • QUOTATION MARK: " (U+0022)
    引號： " （ U+0022 ）

  • ASTERISK: * (U+002A)
    ASTERISK： * （ U+002A ）

  • FULL STOP as the last character: . (U+002E)
    最後一個字元為句號： . （ U+002E ）

  • COLON: : (U+003A)
    冒號： : （ U+003A ）

  • LESS-THAN SIGN: < (U+003C)
    小於號： < （ U+003C ）

  • GREATER-THAN SIGN: > (U+003E)
    大於符號： > （ U+003E ）

  • QUESTION MARK: ? (U+003F)
    問號： ? （ U+003F ）

  • REVERSE SOLIDUS: \ (U+005C)
    反向固相線： \ （ U+005C ）

  • VERTICAL LINE: | (U+007C)
    垂直線： | （ U+007C ）

  • DEL (U+007F) 德爾 （ U+007F ）

  • C0 range (U+0000 … U+001F)
    C0 範圍 （ U+0000 … U+001F ）

  • C1 range (U+0080 … U+009F)
    C1 範圍 （ U+0080 … U+009F ）

  • Private Use Area (U+E000 … U+F8FF)
    私人使用區 （ U+E000 … U+F8FF ）

  • All Unicode Non Characters, specifically:
    所有 Unicode 非字元，特別是：

    • The 32 contiguous characters in the Basic Multilingual Plane (U+FDD0 … U+FDEF)
      基本多語言平面 （ U+FDD0 … U+FDEF ） 中的 32 個連續字元

    • The last two code points of the Basic Multilingual Plane (U+FFFE and U+FFFF)
      基本多語言平面的最後兩個代碼點 （ U+FFFE 和 U+FFFF ）

    • The last two code points at the end of the Supplementary Planes (U+1FFFE, U+1FFFF … U+EFFFE, U+EFFFF)
      補充平面末尾的最後兩個碼位 （ U+1FFFE, U+1FFFF … U+EFFFE, U+EFFFF ）

  • Specials (U+FFF0 … U+FFFF) 特價商品 （ U+FFF0 … U+FFFF ）

  • Supplementary Private Use Area-A (U+F0000 … U+FFFFF)
    補充私人使用區-A （ U+F0000 … U+FFFFF ）

  • Supplementary Private Use Area-B (U+100000 … U+10FFFF)
    補充私人使用區-B （ U+100000 … U+10FFFF ）

  Note 注意

  The Unicode Character Database [uax44] also includes a list of deprecated characters. EPUB creators are advised to avoid these characters, as well, as it is expected that EPUB conformance checkers will flag their use.
  Unicode 字元資料庫 [ uax44] 還包括已棄用字元的清單。建議 EPUB 建立者也避免使用這些字元，因為預計 EPUB 一致性檢查器會標記它們的使用。

• For compatibility with older reading systems, file names SHOULD NOT contain SPACE (U+0020) characters.
  為了與較舊的讀取系統相容，檔名不應包含空格 （U+0020） 字元。

• All file names within the same directory MUST be unique following Unicode canonical normalization [uax15] and then full case folding [unicode]. (Refer to Unicode Canonical Case Fold Normalization Step [charmod-norm] for more information.)
  同一目錄中的所有檔名必須是唯一的，遵循 Unicode 規範化 [uax15]，然後全寫摺疊 [unicode]。（有關詳細資訊，請參閱 Unicode 規範大小寫摺疊規範化步驟 [charmod-norm]。

To derive the file path, given a file or directory file in the OCF abstract container, apply the following steps (expressed using the terminology of [infra]):
要派生文件路徑，給定 OCF 抽象容器中的文件或目錄檔，請應用以下步驟（使用 [ infra] 的術語表示）：

1. Let path be an empty list.
   讓path為空清單。
2. Let current be file. 讓 current 成為檔。
3. While current is not the root directory:
   雖然 current 不是根目錄：
   1. prepend the file name of current to path;
      將 current 的檔名前置到 path;
   2. set current to the parent directory of current.
      將 Current 設定為 Current 的父目錄。
4. Return the concatenation of path using the U+002F (/) character.
   使用 U+002F (/) 字元返回路徑的串聯。

The container root URL is the URL [url] of the root directory. It is implementation-specific, but EPUB creators MUST assume it has the following properties:
容器根 URL 是根目錄的 URL [ url]。它是特定於實現的，但 EPUB 建立者必須假定它具有以下屬性：

• The result of parsing "/" with the container root URL as base is the container root URL.
  以容器根 URL 為基的解析 「 / 的結果是容器根 URL。
• The result of parsing ".." with the container root URL as base is the container root URL.
  以容器根 URL 為基的解析 「 .. 的結果是容器根 URL。

The content URL of a file or directory in the OCF abstract container is the result of parsing the file's file path with the container root URL as base.
OCF 抽象容器中檔或目錄的內容 URL 是以容器根 URL 為基檔路徑解析檔路徑的結果。

A string url is a valid-relative-ocf-URL-with-fragment string if it is a path-relative-scheme-less-url string, optionally followed by U+0023 (#) and a url-fragment string, and if the following steps return true:
如果字串 url 是 path-relative-scheme-less-url 字串，則該字串是 valid-relative-ocf-URL-with-fragment 字符串，可以選擇後跟 U+0023 (#) 和 url-fragment 字符串，並且如果以下步驟返回 true：

1. Set the container root URL to https://a.example.org/A/.
   將容器根 URL 設定為 https://a.example.org/A/ 。

   Explanation 解釋

   The goal of the algorithm is to detect whether url could be seen as "leaking" outside the container. To do that, the standard URL parsing algorithm is used with an artificial root URL; the detection of the "leak" is done by comparing the result of the parsing with the presence of the first test path segment (A). (Note that the artificial container root URL wilfully violates, for the purpose of this algorithm, the required properties by using that first test path segment.)

2. Let base be the base URL that must be used to parse url as defined by the context (document or environment) where url is used, and according to the content URL of the package document (see 5.2 Parsing URLs in the package document).
   設base為必須用於解析 url 的基 URL，該 URL 由使用 url 的上下文（文檔或環境）定義，並根據包文檔的內容 URL（參見 5.2 解析包文檔中的 URL）。

   Explanation 解釋

   In the case of a URL in the package document the base variable is set to the content URL of the package document. In the case of a document within the META-INF directory, the base variable is set to the container root URL (see 4.2.6.2 Parsing URLs in the META-INF directory). In the case of a URL in an XHTML content document, the base URL used for parsing is defined by the HTML standard. Typically, it will be the content URL of the content document (unless the discouraged base element is used).

3. Let testURLRecord be the result of applying the URL parser to url, with base.
   讓 testURLRecord 是將 URL 解析器應用於 url 的結果，帶有 base。
4. Let testURLStringA be the result of applying the URL Serializer to testURLRecord.
   讓 testURLStringA 是將 URL 序列化程式應用於 testURLRecord 的結果。

5. Set the container root URL to https://b.example.org/B/.
   將容器根 URL 設定為 https://b.example.org/B/ 。

   Explanation 解釋

   The reasons to repeat the same steps twice with different, and artificial, settings of the container root URL is to avoid collision which may occur if the url string also includes /A/. Consider, for example, the case where url is ../../A/doc.xhtml.

6. Set base to be the base URL that must be used to parse url as defined by the context (document or environment) where url is used, and according to the content URL of the package document (see 5.2 Parsing URLs in the package document).
   將base設置為必須用於解析 url 的基 URL，該 URL 由使用 url 的上下文（文檔或環境）定義，並根據包文檔的內容 URL（參見 5.2 解析包文檔中的 URL）。
7. Set testURLRecord to be the result of applying the URL parser to url, with base.
   將 testURLRecord 設置為將 URL 解析器應用於 url 的結果，並帶有 base。
8. Let testURLStringB be the result of applying the URL Serializer to testURLRecord.
   讓 testURLStringB 是將 URL 序列化程式應用於 testURLRecord 的結果。

9. If testURLStringA does not start with https://a.example.org/ or testURLStringB does not start with https://b.example.org/, return true.
   如果 testURLStringA 不以 開頭 https://a.example.org/ ，或者 testURLStringB 不以 https://b.example.org/ 開頭，則返回 true。

   Explanation 解釋

   If any of the result does not share the test URL host, it means that url, or its base URL (for example, in HTML, if it is explicitly set with the base element), was absolute and points outside the container. This is acceptable.

10. If testURLStringA starts with https://a.example.org/A/ and testURLStringB starts with https://b.example.org/B/, return true.
    如果 testURLStringA 以 開頭 https://a.example.org/A/ ，而 testURLStringB 以 https://b.example.org/B/ 開頭，則返回 true。

    Explanation 解釋

    The presence of the first test path segments (A, respectively B) indicate that the URL doesn't leak outside the container.

11. Return false. 返回 false。

In the OCF abstract container, any URL string MUST be an absolute-url-with-fragment string or a valid-relative-ocf-URL-with-fragment string.
在 OCF 抽象容器中，任何 URL 字串都必須是 absolute-url-with-fragment 字串或 valid-relative-ocf-URL-with-fragment 字符串。

In addition, all relative-URL-with-fragment strings [url] MUST, after parsing, be equal to the content URL of an existing file in the OCF abstract container.
此外，所有 relative-URL-with-fragment 字串 [ url] 在解析後必須等於 OCF 抽象容器中現有檔的內容 URL。

An OCF ZIP container uses the ZIP format as specified by [zip], but with the following constraints and clarifications:
OCF ZIP 容器使用 [ zip] 指定的 ZIP 格式，但具有以下約束和說明：

• The contents of the OCF ZIP container MUST be a conforming OCF abstract container.
  OCF ZIP容器的內容必須是符合OCF抽象容器的規範。

• OCF ZIP containers MUST NOT use the features in the ZIP application note [zip] that allow ZIP files to be spanned across multiple storage media or be split into multiple files.
  OCF ZIP容器不得使用ZIP應用說明[zip]中的功能，這些功能允許ZIP檔跨多個存儲介質或拆分為多個檔。

• OCF ZIP containers MUST include only stored (uncompressed) and Deflate-compressed ZIP entries within the ZIP archive.
  OCF ZIP 容器必須僅包含 ZIP 存檔中存儲的（未壓縮）和 Deflate 壓縮的 ZIP 條目。

• OCF ZIP containers MAY use the ZIP64 extensions defined as "Version 1" in section V, subsection G of the application note [zip] and SHOULD use only those extensions when the content requires them.
  OCF ZIP容器可以使用應用筆記[zip]第五節G小節中定義為“版本1”的ZIP64擴展，並且應僅在內容需要時使用這些擴展。

• OCF ZIP containers MUST NOT use the encryption features defined by the ZIP format; instead, encryption MUST be done using the features described in 4.2.6.3.2 Encryption file (encryption.xml).
  OCF ZIP容器不得使用ZIP格式定義的加密功能;相反，必須使用 4.2.6.3.2 加密檔 （ encryption.xml ） 中描述的功能進行加密。

• OCF ZIP containers MUST encode file system names using UTF-8 [unicode].
  OCF ZIP 容器必須使用UTF-8 [ unicode] 對檔案系統名稱進行編碼。

The following constraints apply to specific fields in the OCF ZIP container archive:
以下約束適用於OCF ZIP容器存檔中的特定欄位：

• In the local file header table, EPUB creators MUST set the version needed to extract fields to the values 10, 20 or 45 to match the maximum version level needed by the given file (e.g., 20 for Deflate, 45 for ZIP64).
  在本地檔頭表中，EPUB 建立者必須將 version needed to extract 字段設置為值 10 ， 20 或 45 匹配給定檔所需的最大版本級別（例如， 20 對於Deflate， 45 對於 ZIP64）。

• In the local file header table, EPUB creators MUST set the compression method field to the values 0 or 8.
  在本地檔案頭表中，EPUB 建立者必須將 compression 方法欄位設定為值 0 或 8 .

EPUB creators MUST include the mimetype file as the first file in the OCF ZIP container. In addition:
EPUB 建立者必須將該 mimetype 檔作為 OCF ZIP 容器中的第一個檔包含在內。另外：

• The contents of the mimetype file MUST be the MIME media type [rfc2046] string application/epub+zip encoded in US-ASCII [us-ascii].
  mimetype 文件的內容必須是以 US-ASCII [us-ascii] 編碼的 MIME 媒體類型 [ rfc2046] 字串 application/epub+zip 。
• The mimetype file MUST NOT contain any leading or trailing padding or white space.
  檔 mimetype 不得包含任何前導或尾隨填充或空格。
• The mimetype file MUST NOT begin with the Unicode byte order mark U+FEFF.
  mimetype 檔不得以 Unicode 位元組順序標記 U+FEFF 開頭。
• EPUB creators MUST NOT compress or encrypt the mimetype file.
  EPUB 建立者不得壓縮或加密 mimetype 檔。
• EPUB creators MUST NOT include an extra field in its ZIP header.
  EPUB 建立者不得在其 ZIP 標頭中包含額外的欄位。

EPUB creators MUST derive the key used in the obfuscation algorithm from the unique identifier.
EPUB 建立者必須從唯一標識符派生混淆演算法中使用的密鑰。

All white space characters, as defined in section 2.3 of the XML 1.0 specification [xml], MUST be removed from this identifier — specifically, the Unicode code points U+0020, U+0009, U+000D and U+000A.
必須從此標識碼中刪除 XML 1.0 規範 [ xml 第 2.3 節中定義的所有空格字元 — 具體而言，是 Unicode 碼位 U+0020 、 U+0009 和 U+000D U+000A 。

EPUB creators MUST generate a SHA-1 digest of the UTF-8 representation of the resulting string as specified by the Secure Hash Standard [fips-180-4]. They can then use this digest as the key for the algorithm.
EPUB 建立者必須按照安全哈希標準 [fips-180-4] 的規定，生成結果字串的 UTF-8 表示形式的 SHA-1 摘要。然後，他們可以將此摘要用作演算法的金鑰。

The algorithm employed to obfuscate fonts consists of modifying the first 1040 bytes (~1KB) of the font file. (In the unlikely event that the font file is less than 1040 bytes, this process will modify the entire file.)
用於混淆字體的演算法包括修改字體檔的前 1040 位元組 （~1KB）。（萬一字體檔小於1040位元組，此過程將修改整個檔。

To obfuscate the original data, store, as the first byte of the embedded font, the result of performing a logical exclusive or (XOR) on the first byte of the raw font file and the first byte of the obfuscation key.
若要對原始數據進行模糊處理，請將對原始字體檔的第一個字節和混淆密鑰的第一個字節執行邏輯互斥 OR （XOR） 的結果存儲為嵌入字體的第一個字節。

Repeat this process with the next byte of source and key and continue for all bytes in the key. At this point, the process continues starting with the first byte of the key and 21st byte of the source. Once 1040 bytes are encoded in this way (or the end of the source is reached), directly copy any remaining data in the source to the destination.
對源和鍵的下一個字節重複此過程，並對鍵中的所有位元組繼續。此時，該過程從金鑰的第一個字節和源的第 21 個字節開始繼續。以這種方式編碼 1040 位元組后（或到達源的末尾），直接將源中的任何剩餘數據複製到目標。

EPUB creators MUST obfuscate fonts before compressing and adding them to the OCF ZIP container. Note that as obfuscation is not encryption, this requirement is not a violation of the one in 4.2.6.3.2 Encryption file (encryption.xml) to compress fonts before encrypting them.
EPUB 建立者在壓縮字體並將其添加到 OCF ZIP 容器之前必須對字體進行模糊處理。請注意，由於混淆不是加密，因此此要求不違反 4.2.6.3.2 加密檔 （ encryption.xml ） 中在加密字體之前壓縮字體的要求。

The following pseudo-code exemplifies the obfuscation algorithm.
以下偽代碼舉例說明瞭混淆演算法。

1. set ocf to OCF ZIP container file
   將 ocf 設置為 OCF ZIP 容器檔
2. set source to font file
   將源設置為字體檔
3. set destination to obfuscated font file
   將目標設置為混淆字體檔
4. set keyData to key for file
   將keyData設定為文件的鍵
5. set outer to 0 將 outer 設置為 0
6. while outer < 52 and not (source at EOF)
   而外< 52 而不是（來源於 EOF）
   1. set inner to 0 將 inner 設置為 0
   2. while inner < 20 and not (source at EOF)
      而內部< 20 而不是（來源於 EOF）
      1. read 1 byte from source (Assumes read advances file position)
         從源讀取 1 個字節（假定讀取推進檔案位置）
      2. set sourceByte to result of read
         將 sourceByte 設定為讀取結果
      3. set keyByte to byte inner of keyData
         將keyByte設置為keyData的內部位元組
      4. set obfuscatedByte to (sourceByte XOR keyByte)
         將 obfuscatedByte 設置為 （sourceByte XOR keyByte）
      5. write obfuscatedByte to destination
         將 obfuscatedByte 寫入目標
      6. increment inner 增量內部
      end while 結束而
   3. increment outer 增量外部
   end while 結束而
7. if not (source at EOF) then
   如果不是（來源於 EOF），那麼
   1. read source to EOF 將原始碼讀取到 EOF
   2. write result of read to destination
      讀取到目標的寫入結果
   end if 如果結束
8. Deflate destination 放氣目的地
9. store destination as source in ocf
   在 OCF 中將目標存儲為源

Although not technically encrypted data, all obfuscated fonts MUST have an entry in the encryption.xml file accompanying the EPUB publication (see 4.2.6.3.2 Encryption file (encryption.xml)).
儘管不是技術加密數據，但所有混淆字體都必須在 EPUB 出版物隨附 encryption.xml 的檔中有一個條目（請參閱 4.2.6.3.2 加密檔 （ encryption.xml ））。

EPUB creators MUST specify an EncryptedData element for each obfuscated font. Each EncryptedData element MUST contain a child EncryptionMethod element whose Algorithm attribute has the value http://www.idpf.org/2008/embedding. The presence of this attribute signals the use of the algorithm described in this specification.
EPUB 建立者必須為每種混淆字體指定一個 EncryptedData 元素。每個 EncryptedData 元素必須包含一個子 EncryptionMethod 元素，其 Algorithm 屬性的值 http://www.idpf.org/2008/embedding 為 。此屬性的存在表示使用本規範中描述的演算法。

EPUB creators MUST list the path to the obfuscated font in the CipherReference child of the CipherData element. As the obfuscation algorithm is restricted to fonts, the URI attribute of the CipherReference element MUST reference a Font core media type resource.
EPUB 建立者必須在 CipherData 元素的 CipherReference 子元素中列出混淆字體的路徑。由於混淆演算法僅限於字體，因此 CipherReference 元素的 URI 屬性必須引用字體核心媒體類型資源。

To prevent trivial copying of the embedded font to other EPUB publications, EPUB creators MUST NOT provide the obfuscation key in the encryption.xml file.
為防止將嵌入字體複製到其他 EPUB 出版物，EPUB 建立者不得在 encryption.xml 檔中提供混淆密鑰。

Specifies the base direction [bidi] of the textual content and attribute values of the carrying element and its descendants.
指定承載元素及其後代的文本內容和屬性值的基本方向 [ bidi]。

Allowed values are: 允許的值為：

• ltr — left-to-right base direction;
  ltr — 從左到右的基本方向;
• rtl — right-to-left base direction; and
  rtl — 從右到左的基本方向;和
• auto — base direction is determined using the Unicode Bidi Algorithm [bidi].
  auto — 基方向使用 Unicode 雙向演算法 [ bidi] 確定。

Reading systems will assume the value auto when EPUB creators omit the attribute or use an invalid value.
當 EPUB 建立者省略屬性或使用無效值時，讀取系統將假定該值 auto 。

Allowed on: collection, dc:contributor, dc:coverage, dc:creator, dc:description, dc:publisher, dc:relation, dc:rights, dc:subject, dc:title, meta and package.
允許在： collection 、 、 、 dc:contributor dc:coverage dc:creator dc:description dc:publisher dc:relation dc:rights dc:subject dc:title meta 和 package 。

A valid URL string [url] that references a resource.
引用資源的有效 URL 字串 [ url]。

The URL string MUST NOT reference resources via elements in the package document (e.g., via a manifest item or spine itemref declaration).
URL 字串不得通過包文檔中的元素（例如，通過清單 item 或主 itemref 幹聲明）引用資源。

Allowed on: item and link.
允許在： item 和 link 。

The ID [xml] of the element, which MUST be unique within the document scope.
元素的ID[xml]，在文件範圍內必須是唯一的。

Allowed on: collection, dc:contributor, dc:coverage, dc:creator, dc:date, dc:description, dc:format, dc:identifier, dc:language, dc:publisher, dc:relation, dc:rights, dc:source, dc:subject, dc:title, dc:type, item, itemref, link, manifest, meta, package and spine.
允許在： collection ， ， dc:contributor ， ， dc:coverage dc:creator 和 dc:date dc:description dc:format dc:identifier dc:language dc:publisher dc:relation dc:rights dc:source dc:subject dc:title dc:type item itemref link manifest meta package spine .

A media type [rfc2046] that specifies the type and format of the referenced resource.
指定引用資源的類型和格式的媒體類型 [ rfc2046]。

Allowed on: item and link.
允許在： item 和 link 。

A space-separated list of property values.
以空格分隔的屬性值清單。

Refer to each element's definition for the reserved vocabulary for the attribute.
有關屬性的保留詞彙表，請參閱每個元素的定義。

Allowed on: item, itemref and link.
允許在： item 與 itemref link .

Establishes an association between the current expression and the element or resource identified by its value. EPUB creators MUST use as the value a path-relative-scheme-less-URL string, optionally followed by U+0023 (#) and a URL-fragment string that references the resource or element they are describing.
在當前表達式與其值標識的元素或資源之間建立關聯。EPUB 建立者必須使用 path-relative-scheme-less-URL 字串作為值，（可選）後跟 U+0023 (#) 引用他們所描述的資源或元素的 URL-fragment 字符串。

The refines attribute is OPTIONAL depending on the type of metadata expressed. When omitted, the element defines a primary expression.
該 refines 屬性是OPTIONAL，具體取決於所表達的元數據類型。省略時，該元素定義主表達式。

When creating expressions about a publication resource, the refines attribute SHOULD specify a fragment identifier that references the ID [xml] of the resource's manifest entry.
創建有關發佈資源的表示式時， refines 該屬性應指定引用資源清單條目的ID[xml]的片段識別碼。

Refinement chains MUST NOT contain circular references or self-references.
精簡鏈不得包含迴圈引用或自引用。

Allowed on: link and meta.
允許在： link 和 meta 。

Specifies the language of the textual content and attribute values of the carrying element and its descendants, as defined in section 2.12 Language Identification of [xml]. The value of each xml:lang attribute MUST be a well-formed language tag [bcp47].
指定承載元素及其後代的文本內容和屬性值的語言，如第 2.12 節 [ xml 的語言標識中所定義。每個 xml:lang 屬性的值必須是格式正確的語言標記 [bcp47]。

Allowed on: collection, dc:contributor, dc:coverage, dc:creator, dc:description, dc:publisher, dc:relation, dc:rights, dc:subject, dc:title, meta and package.
允許在： collection 、 、 、 dc:contributor dc:coverage dc:creator dc:description dc:publisher dc:relation dc:rights dc:subject dc:title meta 和 package 。

The metadata element encapsulates meta information.
該 metadata 元素封裝元資訊。

Element Name: 元素名稱：

metadata

Usage: 用法：

REQUIRED first child of package.
必需的第一個子項 package 。

Attributes: 屬性：

None 沒有

Content Model: 內容模型：

In any order: 按任意順序：

• dc:identifier [1 or more]

• dc:title [1 or more]

• dc:language [1 or more]

• Dublin Core Optional Elements [0 or more]

• meta [1 or more]

• OPF2 meta [0 or more] (legacy)
  OPF2 meta [0 or more] （舊版）

• link [0 or more]

The package document metadata element has two primary functions:
包文件 metadata 元素有兩個主要功能：

1. to provide a minimal set of meta information for reading systems to use to internally catalogue an EPUB publication and make it available to a user (e.g., to present in a bookshelf).
   為閱讀系統提供一組最小的元資訊，用於對 EPUB 出版物進行內部編目並提供給使用者（例如，在書架上展示）。

2. to provide access to all rendering metadata needed to control the layout and display of the content (e.g., fixed-layout properties).
   提供對控制內容佈局和顯示所需的所有渲染元數據（例如，固定佈局屬性）的訪問。

The package document does not provide complex metadata encoding capabilities. If EPUB creators need to provide more detailed information, they can associate metadata records (e.g., that conform to an international standard such as [onix] or are created for custom purposes) using the link element. This approach allows reading systems to process the metadata in its native form, avoiding the potential problems and information loss caused by translating to use the minimal package document structure.
包文檔不提供複雜的元數據編碼功能。如果 EPUB 建立者需要提供更詳細的資訊，他們可以使用該 link 元素關聯元數據記錄（例如，符合 [ onix] 等國際標準或為自定義目的創建的元數據記錄）。這種方法允許讀取系統以本機形式處理元數據，從而避免了因使用最小包文檔結構進行翻譯而導致的潛在問題和信息丟失。

In keeping with this philosophy, the package document only has the following minimal metadata requirements: it MUST contain the [dcterms] dc:title, dc:identifier, and dc:language elements together with the [dcterms] dcterms:modified property. All other metadata is OPTIONAL.
為了與這一理念保持一致，包文檔僅具有以下最低元數據要求：它必須包含 [ dcterms] dc:title 、 dc:identifier 和 dc:language 元素以及 [ dcterms] dcterms:modified 屬性。所有其他元數據都是可選的。

The meta element provides a generic mechanism for including metadata properties from any vocabulary. Although EPUB creators MAY use this mechanism for any metadata purposes, they will typically use it to include rendering metadata defined in EPUB specifications.
該 meta 元素提供了一種通用機制，用於包含來自任何詞彙表的元數據屬性。儘管 EPUB 建立者可以將此機制用於任何元數據目的，但他們通常會使用它來包含 EPUB 規範中定義的呈現元數據。

The Dublin Core elements [dcterms] and meta element have mandatory child text content [dom]. In the descriptions for these elements, this specification refers to this content as the element's value.
Dublin Core 元素 [ dcterms] 和 meta 元素具有必需的子文本內容 [ dom]。在這些元素的描述中，此規範將此內容稱為元素的值。

These elements MUST have non-empty values after leading and trailing ASCII whitespace [infra] is stripped (i.e., they must consist of at least one non-whitespace character).
在前導和尾隨 ASCII 空格 [ infra] 被剝離后，這些元素必須具有非空值（即，它們必須包含至少一個非空格字元）。

Whitespace within these element values is not significant. Sequences of one or more whitespace characters are collapsed to a single space [infra] during processing .
這些元素值中的空格並不重要。在處理過程中，一個或多個空格字元的序列被摺疊到單個空格 [ infra] 。