How Does the Detect ASCII Text Feature Work?
This article applies to all MetaDefender Core V5 releases deployed on Windows or Linux systems
Overview
The "Detect ASCII Text" configuration helps classify files as ASCII-based text files based on their character content. This feature distinguishes between ASCII and non-ASCII (binary or extended encoding) by analyzing the characters in the file.
Behavior Summary
When this configuration is enabled, the system scans the content of a file to determine whether it qualifies as ASCII text. The classification depends on the percentage of non-printable characters found within the file.
However, not all control characters are treated as non-printable. Some characters typically seen in text files are allowed and still result in the file being recognized as ASCII.
What Characters Are Considered Printable?
The following ASCII control characters are treated as printable in this feature:
These characters are allowed because:
- They produce visible effects (e.g., spacing or new lines).
- They are common in plain text files and source code.
Non-Printable Characters (Excluded from ASCII Detection)
The system considers the following characters as non-printable:
- ASCII codes 1–8
- 11 (Vertical Tab)
- 12 (Form Feed)
- ASCII codes 14–31
- 127 (Delete)
Presence of these characters beyond a configured threshold can cause the file to not be classified as an ASCII text file.
Examples
✅ File Detected as ASCII:
- File contains only tabs, spaces, and line breaks.
- Even with a high number of tabs (\t), it is still considered ASCII.
❌ File Not Detected as ASCII:
- File contains a high percentage of extended characters (e.g., many occurrences of characters like € or other non-ASCII symbols) or disallowed control characters may exceed the threshold and not be classified as ASCII.
FAQ
> Why isn't the tab character treated as non-printable?
Tabs (0x09) are widely used in plain text files for formatting and are visually represented. Hence, they are treated as printable.
> Can we change what characters are considered non-printable?
The default set of printable characters is built into the FileType engine and cannot be changed via configuration in the UI.
References
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