An RCS file is an ASCII file. Its contents are described by the grammar below. The text is free format, i.e., spaces, tabs and new lines have no significance except in strings. Strings are enclosed by '@'. If a string contains a '@', it must be doubled.

The meta syntax uses the following conventions: '|' (bar) separates alternatives; '{' and '}' enclose optional phrases; '{' and '}*' enclose phrases that may be repeated zero or more times; '{' and '}+' enclose phrases that must appear at least once and may be repeated; '<' and '>' enclose nonterminals.

::= {}* {}*

::= head {};

branch {};

access {}*;

symbols { : }*;

locks { : }*;

comment {};

::=

date ;

author ;

state {};

branches {}*;

next {};

::= desc

::=

log

text

::= {{.}}+

::= 0 | 1 | ... | 9

::= {}*

::= A | B | ... | Z | a | b | ... | z

::= Any printing ASCII character except space, tab,

carriage return, new line, and .

::= ; | : | , | @

::= @{any ASCII character, with '@' doubled}*@

Identifiers are case sensitive. Keywords are in lower case only. The sets of keywords and identifiers may overlap.

The nodes form a tree. All nodes whose numbers consist of a single pair (e.g., 2.3, 2.1, 1.3, etc.) are on the "trunk", and are linked through the next field in order of decreasing numbers. The head field in the node points to the head of that sequence (i.e., contains the highest pair). The branch node in the admin node indicates the default branch (or revision) for most RCS operations. If empty, the default branch is the highest branch on the trunk.

All nodes whose numbers consist of 2n fields (n>2) (e.g., 3.1.1.1, 2.1.2.2, etc.) are linked as follows. All nodes whose first (2n)-1 number fields are identical are linked through the next field in order of increasing numbers. For each such sequence, the node whose number is identical to the first 2(n-1) number fields of the deltas on that sequence is called the branchpoint. The branches field of a node contains a list of the numbers of the first nodes of all sequences for which it is a branchpoint. This list is ordered in increasing numbers.

Example:

Head

|

|

v

---------

/ \ / \ | | / \ / \

/ \ / \ | 2.1 | / \ / \

/ \ / \ | | / \ / \

/1.2.1.3\ /1.3.1.1\ | | /1.2.2.2\ /1.2.2.1.1.1\

--------- --------- --------- --------- -------------

^ ^ | ^ ^

| | | | |

| | v | |

/ \ | --------- / \ |

/ \ | \ 1.3 / / \ |

/ \ ---------\ / / \-----------

/1.2.1.1\ \ / /1.2.2.1\

--------- \ / ---------

^ | ^

| | |

| v |

| --------- |

| \ 1.2 / |

----------------------\ /---------

\ /

\ /

|

|

v

---------

\ 1.1 /

\ /

\ /

\ /

Fig. 1: A revision tree