@Experimental
    public final PoolingAsyncClientConnectionManagerBuilder setMessageMultiplexing(final boolean messageMultiplexing) {
        this.messageMultiplexing = messageMultiplexing;
        return this;
    }
Use experimental connections pool implementation that acts as a caching facade
in front of a standard connection pool and shares already leased connections
to multiplex message exchanges over active HTTP/2 connections.
<p>
Please note this flag has no effect on HTTP/1.1 and HTTP/1.0 connections.
<p>
This feature is considered experimenal

@since 5.5
@return this instance.
httpclient5/src/main/java/org/apache/hc/client5/http/impl/nio/PoolingAsyncClientConnectionManagerBuilder.java