Why is this an issue?

Non-encoded control characters and whitespace characters are often injected in the source code because of a bad manipulation. They are either invisible or difficult to recognize, which can result in bugs when the string is not what the developer expects. If you actually need to use a control character use their encoded version (ex: ASCII \n,\t,…​ or Unicode U+000D, U+0009,…​).

This rule raises an issue when the following characters are seen in a literal string:

No issue will be raised on the simple space character. Unicode U+0020, ASCII 32.

Noncompliant code example

String tabInside = "A	B";  // Noncompliant, contains a tabulation
String zeroWidthSpaceInside = "foo​bar"; // Noncompliant, it contains a U+200B character inside
char tab = '	';

Compliant solution

String tabInside = "A\tB";  // Compliant, uses escaped value
String zeroWidthSpaceInside = "foo\u200Bbar";  // Compliant, uses escaped value
char tab = '\t';