# EPUBCheck NCX-004: NCX identifier (dtb:uid metadata)…

Source: https://epublab.com/epubcheck/ncx-004/ (updated 2026-11-03)

EPUBCheck NCX-004 is a usage message: “NCX identifier ("dtb:uid" metadata) should not contain leading or trailing whitespace.” The NCX's dtb:uid value has spaces or line breaks before or after it.

- Official message (EPUBCheck 5.4.0): NCX identifier ("dtb:uid" metadata) should not contain leading or trailing whitespace.
- Default severity: Usage

## Typical causes

- Pretty-printed XML that put the value on its own line.

## How to fix it

- Remove the whitespace around the value of dtb:uid.

Message text and severity: EPUBCheck (W3C, BSD-3-Clause). Explanation: EPUBLab.