But not by any means incompatible with his fealty

From Robert Fawtier’s The Capetian Kings of France (pg63-64):

(Maybe it’s just my odd sense of humor but I imagine the negotiation and composition processes for this agreement as scenes from a Mel Brooks movie and am terribly amused)

On 10 March 1103 Robert of Jerusalem, Count of Flanders, made a treaty at Dover with King Henry I of England against King Philip I of France.  The second article of this treaty admirably illustrates the attitude of the great vassals of the Capetians.  Homage was a solemn obligation they had freely entered into.  It tied them to the king, and they were bound by oath not to break it.  The most they were capable of attempting was seeking means to circumvent it.  And so the Count of Flanders assured the King of England of his support, “saving his fealty to Philip, King of France, in such wise that if King Philip shall intend to invade the realm of England, Count Robert will seek to prevent King Philip in every way possible, by his counsel and by his prayers, but not by any means incompatible with his fealty, nor by plotting against him, nor by offering him bribes.  And if King Philip shall come to England, and shall bring Count Robert with him, Count Robert will take the smallest possible retinue, but not so small that he may thereby incur the forfeiture of his fief to the King of France.”