1. A method for coding/decoding structured documents comprising structural items which include one or more elements, the method comprising: generating at least one unified model representative of the structure of a type of element, wherein the unified model is generated on the basis of at least one structured configuration document, wherein the unified model includes a list of starting items, following items and transitions between respective starting and following items in a first priority level, and wherein the unified model comprises statistical information on transitions made in the occurrences of the element type within the at least one structured configuration document; modifying the unified model into a modified unified model so as to improve compression efficiency, using the statistical information on transitions, wherein the modification comprises grouping together at least two of the transitions between a same starting item and a group of following items into a single transition from the same starting item in the first priority level and assigning a second priority level for one or more transitions within the grouping; generating configuration data for configuring a coding/decoding processor, wherein the configuration data includes said modified unified model; and generating at least one coding/decoding table using the modified unified model by associating a coding value with each transition of the modified unified model, wherein the coding values associated with grouped transitions are composite coding values made of a first priority coding value that is the same for all the grouped transitions combined with a second priority coding value that is different from one of the grouped transitions to another grouped transition.