containsHeaderString makes sense in HttpHeaders
diff --git a/jaxrs-api/src/main/java/jakarta/ws/rs/core/HttpHeaders.java b/jaxrs-api/src/main/java/jakarta/ws/rs/core/HttpHeaders.java
index 2d32cbe..f77a334 100644
--- a/jaxrs-api/src/main/java/jakarta/ws/rs/core/HttpHeaders.java
+++ b/jaxrs-api/src/main/java/jakarta/ws/rs/core/HttpHeaders.java
@@ -61,6 +61,23 @@
public String getHeaderString(String name);
/**
+ * Checks whether a header with a specific name and value (or item of the comma-separated value list) exists.
+ *
+ * Each single header value is converted to String using a {@link jakarta.ws.rs.ext.RuntimeDelegate.HeaderDelegate} if one
+ * is available via {@link jakarta.ws.rs.ext.RuntimeDelegate#createHeaderDelegate(java.lang.Class)} for the header value
+ * class or using its {@code toString} method if a header delegate is not available.
+ *
+ * @param name the message header.
+ * @param value the message header value.
+ * @param ignoreCase whether to ignore upper/lower case.
+ * @return {@code true} if and only if a header with the provided name exists having either the exact value or whose
+ * comma-separated header string contains value as a whole word.
+ * @see #getRequestHeaders()
+ * @see #getHeaderString(String)
+ */
+ public boolean containsHeaderString(String name, String value, boolean ignoreCase);
+
+ /**
* Get the values of HTTP request headers. The returned Map is case-insensitive wrt. keys and is read-only. The method
* never returns {@code null}.
*
