Finding a substring using C# with a twist

I have a string that contains the numerous tags of the following form:

<: Entity.FieldGroup.FieldName [| Modifier] :>

I need to find the tags and replace them with some value(s). So for example the text I have might look as follows:

Blah <: Person.Meta.Age :> blah <:       PERSON.meTA.Dependants | CommaList :>

and when replaced look like:

Blah 30 blah Harry, Mary, John

Now the issues are that:

• There may be different amounts of whitespace after and before the opening and closing tags (<: and :>)


• Things may be entered in different case Person vs PERSON, Meta vs meTA


• I cannot "affect" the text around the tags


• There is no predetermined list of tag names ie. Tomorrow might bring Animal.Kind for instance

So from a performance point of view what is the best approach here to extract the tags so I can replace them?

I am concerned that as I replace tags the length of the string I am replacing into changes and thus any offsets won't work and so on. Any suggestions on how to achieve the above elegantly?