Regex float parameters docs (#866)

* Minor documentation for update for regexps when floating params

* Add some additional documentation for ChannelCompatibilityCheck groups

docs/part3/commonstatsmethods.md

@@ -771,9 +771,12 @@ By default, the signal strength is kept floating in the fit with the nominal mod
 
 In the default model built from the datacards, the signal strengths in all channels are constrained to be non-negative. One can allow negative signal strengths in the fits by changing the bound on the variable (option `--rMin=<value>`), which should make the quantity more chisquare-like under the hypothesis of zero signal; this however can create issues in channels with small backgrounds, since total expected yields and PDFs in each channel must be positive.
 
+Optionally, channels can be grouped together by using the option `-g <name_fragment>`, where `<name_fragment>` is a string which is common to all channels to be grouped together. The `-g` option can also be used to set the range for the each POI separately via `-g <name>=<min>,<max>`.
+
 When run with a verbosity of 1, as is the default, the program also prints out the best fit signal strengths in all channels. As the fit to all channels is done simultaneously, the correlation between the other systematic uncertainties is taken into account. Therefore, these results can differ from the ones obtained when fitting each channel separately.
 
 
+
 Below is an example output from <span style="font-variant:small-caps;">Combine</span>,
 
 ```nohighlight

docs/part3/runningthetool.md

@@ -55,7 +55,7 @@ There are a number of useful command-line options that can be used to alter the
 
 -   `--freezeParameters name1[,name2,...]` Will freeze the parameters with the given names to their set values. This option supports the use of regular expression by replacing `name` with `rgx{some regular expression}` for matching to *constrained nuisance parameters* or `var{some regular expression}` for matching to *any* parameter. For example `--freezeParameters rgx{CMS_scale_j.*}` will freeze all constrained nuisance parameters with the prefix `CMS_scale_j`, while `--freezeParameters var{.*rate_scale}` will freeze any parameter (constrained nuisance parameter or otherwise) with the suffix `rate_scale`.
     - Use the option `--freezeParameters allConstrainedNuisances` to freeze all nuisance parameters that have a constraint term (i.e not `flatParams` or `rateParams` or other freely floating parameters).
-    - Similarly, the option `--floatParameters name1[,name2,...]` sets the parameter(s) floating.
+    - Similarly, the option `--floatParameters name1[,name2,...]` sets the parameter(s) floating and also accepts regular expressions.
     - Groups of nuisance parameters (constrained or otherwise), as defined in the datacard, can be frozen using `--freezeNuisanceGroups`. You can also freeze all nuisances that are *not* contained in a particular group using a **^** before the group name (`--freezeNuisanceGroups=^group_name` will freeze everything except nuisance parameters in the group "group_name".)
     - All *constrained* nuisance parameters (not `flatParam` or `rateParam`) can be set floating using `--floatAllNuisances`.