They communicate statements like, Whatever you want is okay. It's all right with me. You decide for me. They ask permission for things that other people just take for granted and go ahead and do. Say what you want straight out instead of asking permission when it is appropriate.
Doormats often have an excess of apologizing for small discomforts.
Those who are around Doormats often recognize their submissiveness and begin to take control of the situation. Giving in to others is consistent with closed family systems which teach manipulation and submissiveness rather than straight communication. When they transgress these family rules and speak out, they feel guilty. They go through life ruled by the guilt that they have internalized. In an open system, energy is spent in promoting change, and there is a balance of power.