diff --git a/jaxrs-api/src/main/java/jakarta/ws/rs/client/ClientRequestContext.java b/jaxrs-api/src/main/java/jakarta/ws/rs/client/ClientRequestContext.java
index 9873f40..70e7af5 100644
--- a/jaxrs-api/src/main/java/jakarta/ws/rs/client/ClientRequestContext.java
+++ b/jaxrs-api/src/main/java/jakarta/ws/rs/client/ClientRequestContext.java
@@ -201,12 +201,13 @@
      * class or using its {@code toString} method if a header delegate is not available.
      *
      * <p>
-     * For example: {@code containsHeaderString("cache-control", "no-store"::equalsIgnoreCase)} will return {@code true} if
+     * For example: {@code containsHeaderString("cache-control", null, "no-store"::equalsIgnoreCase)} will return {@code true} if
      * a {@code Cache-Control} header exists that has the value {@code no-store}, the value {@code No-Store} or the value
      * {@code Max-Age, NO-STORE, no-transform}, but {@code false} when it has the value {@code no-store;no-transform}
      * (missing comma), or the value {@code no - store} (whitespace within value).
      *
      * @param name the message header.
+     * @param valueSeparatorRegex Separates the header value into single values. Defaults to {@code \s*,\s*} when {@code null}.
      * @param valuePredicate value must fulfil this predicate.
      * @return {@code true} if and only if a header with the given name exists, having either a whitespace-trimmed value
      * matching the predicate, or having at least one whitespace-trimmed single value in a comma-separated list of single values.
@@ -214,7 +215,7 @@
      * @see #getHeaderString(String)
      * @since 4.0
      */
-    public boolean containsHeaderString(String name, Predicate<String> valuePredicate);
+    public boolean containsHeaderString(String name, String valueSeparatorRegex, Predicate<String> valuePredicate);
 
     /**
      * Get message date.
diff --git a/jaxrs-api/src/main/java/jakarta/ws/rs/client/ClientResponseContext.java b/jaxrs-api/src/main/java/jakarta/ws/rs/client/ClientResponseContext.java
index 807ede7..8abcc0b 100644
--- a/jaxrs-api/src/main/java/jakarta/ws/rs/client/ClientResponseContext.java
+++ b/jaxrs-api/src/main/java/jakarta/ws/rs/client/ClientResponseContext.java
@@ -93,12 +93,13 @@
      * Checks whether a header with a specific name and value (or item of the comma-separated value list) exists.
      *
      * <p>
-     * For example: {@code containsHeaderString("cache-control", "no-store"::equalsIgnoreCase)} will return {@code true} if
+     * For example: {@code containsHeaderString("cache-control", null, "no-store"::equalsIgnoreCase)} will return {@code true} if
      * a {@code Cache-Control} header exists that has the value {@code no-store}, the value {@code No-Store} or the value
      * {@code Max-Age, NO-STORE, no-transform}, but {@code false} when it has the value {@code no-store;no-transform}
      * (missing comma), or the value {@code no - store} (whitespace within value).
      *
      * @param name the message header.
+     * @param valueSeparatorRegex Separates the header value into single values. Defaults to {@code \s*,\s*} when {@code null}.
      * @param valuePredicate value must fulfil this predicate.
      * @return {@code true} if and only if a header with the given name exists, having either a whitespace-trimmed value
      * matching the predicate, or having at least one whitespace-trimmed single value in a comma-separated list of single values.
@@ -106,7 +107,7 @@
      * @see #getHeaderString(String)
      * @since 4.0
      */
-    public boolean containsHeaderString(String name, Predicate<String> valuePredicate);
+    public boolean containsHeaderString(String name, String valueSeparatorRegex, Predicate<String> valuePredicate);
 
     /**
      * Get the allowed HTTP methods from the Allow HTTP header.
diff --git a/jaxrs-api/src/main/java/jakarta/ws/rs/container/ContainerRequestContext.java b/jaxrs-api/src/main/java/jakarta/ws/rs/container/ContainerRequestContext.java
index 9a50430..b755913 100644
--- a/jaxrs-api/src/main/java/jakarta/ws/rs/container/ContainerRequestContext.java
+++ b/jaxrs-api/src/main/java/jakarta/ws/rs/container/ContainerRequestContext.java
@@ -233,12 +233,13 @@
      * Checks whether a header with a specific name and value (or item of the comma-separated value list) exists.
      *
      * <p>
-     * For example: {@code containsHeaderString("cache-control", "no-store"::equalsIgnoreCase)} will return {@code true} if
+     * For example: {@code containsHeaderString("cache-control", null, "no-store"::equalsIgnoreCase)} will return {@code true} if
      * a {@code Cache-Control} header exists that has the value {@code no-store}, the value {@code No-Store} or the value
      * {@code Max-Age, NO-STORE, no-transform}, but {@code false} when it has the value {@code no-store;no-transform}
      * (missing comma), or the value {@code no - store} (whitespace within value).
      *
      * @param name the message header.
+     * @param valueSeparatorRegex Separates the header value into single values. Defaults to {@code \s*,\s*} when {@code null}.
      * @param valuePredicate value must fulfil this predicate.
      * @return {@code true} if and only if a header with the given name exists, having either a whitespace-trimmed value
      * matching the predicate, or having at least one whitespace-trimmed single value in a comma-separated list of single values.
@@ -246,7 +247,7 @@
      * @see #getHeaderString(String)
      * @since 4.0
      */
-    public boolean containsHeaderString(String name, Predicate<String> valuePredicate);
+    public boolean containsHeaderString(String name, String valueSeparatorRegex, Predicate<String> valuePredicate);
 
     /**
      * Get message date.
diff --git a/jaxrs-api/src/main/java/jakarta/ws/rs/container/ContainerResponseContext.java b/jaxrs-api/src/main/java/jakarta/ws/rs/container/ContainerResponseContext.java
index 70fe218..936f5cc 100644
--- a/jaxrs-api/src/main/java/jakarta/ws/rs/container/ContainerResponseContext.java
+++ b/jaxrs-api/src/main/java/jakarta/ws/rs/container/ContainerResponseContext.java
@@ -123,12 +123,13 @@
      * class or using its {@code toString} method if a header delegate is not available.
      *
      * <p>
-     * For example: {@code containsHeaderString("cache-control", "no-store"::equalsIgnoreCase)} will return {@code true} if
+     * For example: {@code containsHeaderString("cache-control", null, "no-store"::equalsIgnoreCase)} will return {@code true} if
      * a {@code Cache-Control} header exists that has the value {@code no-store}, the value {@code No-Store} or the value
      * {@code Max-Age, NO-STORE, no-transform}, but {@code false} when it has the value {@code no-store;no-transform}
      * (missing comma), or the value {@code no - store} (whitespace within value).
      *
      * @param name the message header.
+     * @param valueSeparatorRegex Separates the header value into single values. Defaults to {@code \s*,\s*} when {@code null}.
      * @param valuePredicate value must fulfil this predicate.
      * @return {@code true} if and only if a header with the given name exists, having either a whitespace-trimmed value
      * matching the predicate, or having at least one whitespace-trimmed single value in a comma-separated list of single values.
@@ -136,7 +137,7 @@
      * @see #getHeaderString(String)
      * @since 4.0
      */
-    public boolean containsHeaderString(String name, Predicate<String> valuePredicate);
+    public boolean containsHeaderString(String name, String valueSeparatorRegex, Predicate<String> valuePredicate);
 
     /**
      * Get the allowed HTTP methods from the Allow HTTP header.
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 782afb5..8895d75 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
@@ -69,12 +69,13 @@
      * class or using its {@code toString} method if a header delegate is not available.
      *
      * <p>
-     * For example: {@code containsHeaderString("cache-control", "no-store"::equalsIgnoreCase)} will return {@code true} if
+     * For example: {@code containsHeaderString("cache-control", null, "no-store"::equalsIgnoreCase)} will return {@code true} if
      * a {@code Cache-Control} header exists that has the value {@code no-store}, the value {@code No-Store} or the value
      * {@code Max-Age, NO-STORE, no-transform}, but {@code false} when it has the value {@code no-store;no-transform}
      * (missing comma), or the value {@code no - store} (whitespace within value).
      *
      * @param name the message header.
+     * @param valueSeparatorRegex Separates the header value into single values. Defaults to {@code \s*,\s*} when {@code null}.
      * @param valuePredicate value must fulfil this predicate.
      * @return {@code true} if and only if a header with the given name exists, having either a whitespace-trimmed value
      * matching the predicate, or having at least one whitespace-trimmed single value in a comma-separated list of single values.
@@ -82,7 +83,7 @@
      * @see #getHeaderString(String)
      * @since 4.0
      */
-    public boolean containsHeaderString(String name, Predicate<String> valuePredicate);
+    public boolean containsHeaderString(String name, String valuleSeparatorRegex, Predicate<String> valuePredicate);
 
     /**
      * Get the values of HTTP request headers. The returned Map is case-insensitive wrt. keys and is read-only. The method