HTML does not allow one to define new text elements; that is, it is not extensible.
XML began to be developed in the 1990s because HTML (hypertext markup language), the basic format for Web pages, does not allow the definition of new text elements; that is, it is not extensible.
How easily extensible is it?
The CertiKOS architecture is also designed to be highly extensible — that is, it can take on new functionalities and be used for different application domains.
As with all lists, it is extensible in the columns it contains, it supports multi-valued fields, and the items in it can be indexed.
Allowing for spacers in a string is what makes it extensible.
Thus far it can only recognize simple characters but it is easily extensible.
Due to its hierarchical integration structure, it is readily extensible to include other relevant similarity measures if available (e.g. enzyme affinities), or to modify a component score (e.g. using compound molecular similarity scores).
In addition, it has been further improved by parallel query processing, it is now extensible with different analysis tools and the installation process can be effortlessly completed with just a few mouse clicks (16).
It is highly extensible, and Linked-Data friendly, so that its limitations could easily be addressed by those with the domain expertise to do so.
Microsoft's.NET transport format fares better in this respect because it has a more flexible type system and instruction set, but it is not extensible, and (for example) has no provision for supporting explicit programmer-specified parallelism.
